Preambles for wake-up receivers

ABSTRACT

This disclosure provides systems, methods and apparatuses for indicating a data rate of a packet. The transmitting device may select the data rate of a data field of the packet to be transmitted to the receiving device, and may select a pattern to embed within a preamble of the packet based on the selected data rate. In some implementations, the transmitting device may select a first structure including a first number of instances of a sequence or its logical complement if the selected data rate is a low data rate, and may select a second structure including a second number of instances of the sequence or its logical complement if the selected data rate is a high data rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority to U.S. Provisional PatentApplication No. 62/557,123 entitled “PREAMBLES FOR WAKE-UP RECEIVERS”filed on Sep. 11, 2017, to U.S. Provisional Patent Application No.62/568,760 entitled “PREAMBLES FOR WAKE-UP RECEIVERS” filed on Oct. 5,2017, and to U.S. Provisional Patent Application No. 62/571,244 entitled“PREAMBLES FOR WAKE-UP RECEIVERS” filed on Oct. 11, 2017, all assignedto the assignee hereof. The disclosures of all prior Applications areconsidered part of and are incorporated by reference in this PatentApplication.

TECHNICAL FIELD

This disclosure relates generally to wireless communications, and morespecifically to preambles for wake-up receivers in wireless devices.

DESCRIPTION OF THE RELATED TECHNOLOGY

A wireless local area network (WLAN) may be formed by one or more accesspoints (APs) that provide a shared wireless medium for use by a numberof client devices. Each AP, which may correspond to a Basic Service Set(BSS), periodically broadcasts beacon frames to enable compatible clientdevices within wireless range of the AP to establish and maintain acommunication link with the WLAN. WLANs that operate in accordance withthe IEEE 802.11 family of standards are commonly referred to as Wi-Finetworks, and client devices that communicate with the AP in a Wi-Finetwork may be referred to as wireless stations (STAs).

Bluetooth technology also allows a number of wireless devices tocommunicate with each other using radio-frequency signals. Althoughsimilar in some aspects to Wi-Fi devices, Bluetooth devices typicallycommunicate with each other without the presence of an AP (or othercentral controller). In addition, although Bluetooth devices typicallyhave shorter wireless ranges than Wi-Fi devices, Bluetooth radios areless expensive and consume less power than Wi-Fi radios. As a result,Bluetooth technology is particularly well suited for applications (suchas the Internet of Things) in which minimizing power consumption may bemore important than achieving high data rates. The Internet of Things(IoT) may refer to a communication system in which a wide variety ofobjects and devices wirelessly communicate with each other.

A wireless device may have a limited amount of battery power. During asleep mode, a wireless device may periodically activate a radio, such asa wake-up receiver (WUR), to listen for and decode messages such as awake-up message. The wake-up message may indicate whether another device(such as an AP) has queued data waiting to be transmitted to thewireless device. In some cases, the wireless device may not successfullydecode the wake-up message.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented as a method for indicating a data rate of a packet tobe transmitted to a receiving device. In some implementations, themethod can be performed by a transmitting device and can includeselecting the data rate of a data field of the packet; selecting apattern to embed within a preamble of the packet based on the selecteddata rate by selecting a first structure if the selected data rate is alow data rate and selecting a second structure if the selected data rateis a high data rate; and transmitting the packet to the receivingdevice, the preamble of the packet including either the first structureor the second structure as the selected pattern. In someimplementations, the first structure can include a first number ofinstances of a sequence or its logical complement, and the secondstructure can include a second number of instances of the sequence orits logical complement. In some aspects, the first structure can includetwo instances of the sequence, and the second structure can include asingle instance of the logical complement of the sequence. In addition,or in the alternative, the second structure can include one or moreinstances of a second sequence or one or more instances of a logicalcomplement of the second sequence, can include one or more instances ofa pad sequence, or both.

In some implementations, the first structure may be configured togenerate one or more positive peaks in a waveform when the firststructure is correlated with a reference pattern, and the secondstructure may be configured to generate a negative peak in the waveformwhen the second structure is correlated with the reference pattern. Insome aspects, the reference pattern may be derived from the sequence byconverting each logical low bit of the sequence to a negative one, andconverting each logical high bit of the sequence to a positive one.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a transmitting device configured toindicate a data rate of a packet to be transmitted to a receivingdevice. In some implementations, the transmitting device can include oneor more processors and a memory storing instructions. Execution of theinstructions can cause the transmitting device to select the data rateof a data field of the packet; to select a pattern to embed within apreamble of the packet based on the selected data rate by selecting afirst structure if the selected data rate is a low data rate andselecting a second structure if the selected data rate is a high datarate; and to transmit the packet to the receiving device, the preambleof the packet including either the first structure or the secondstructure as the selected pattern. In some implementations, the firststructure can include a first number of instances of a sequence or itslogical complement, and the second structure can include a second numberof instances of the sequence or its logical complement. In some aspects,the first structure can include two instances of the sequence, and thesecond structure can include a single instance of the logical complementof the sequence. In addition, or in the alternative, the secondstructure can include one or more instances of a second sequence or oneor more instances of a logical complement of the second sequence, caninclude one or more instances of a pad sequence, or both.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium can storeinstructions that, when executed by one or more processors of anapparatus, cause the apparatus to perform a number of operations. Insome implementations, the number of operations can include selecting adata rate of a data field of a packet to be transmitted to a receivingdevice; selecting a pattern to embed within a preamble of the packetbased on the selected data rate by selecting a first structure if theselected data rate is a low data rate and selecting a second structureif the selected data rate is a high data rate; and transmitting thepacket to the receiving device, the preamble of the packet includingeither the first structure or the second structure as the selectedpattern. In some implementations, the first structure can include afirst number of instances of a sequence or its logical complement, andthe second structure can include a second number of instances of thesequence or its logical complement. In some aspects, the first structurecan include two instances of the sequence, and the second structure caninclude a single instance of the logical complement of the sequence. Inaddition, or in the alternative, the second structure can include one ormore instances of a second sequence or one or more instances of alogical complement of the second sequence, can include one or moreinstances of a pad sequence, or both.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus configured to indicate adata rate of a packet to be transmitted to a receiving device. Theapparatus can include means for selecting the data rate of a data fieldof the packet; means for selecting a pattern to embed within a preambleof the packet based on the selected data rate by selecting a firststructure if the selected data rate is a low data rate and selecting asecond structure if the selected data rate is a high data rate; andmeans for transmitting the packet to the receiving device, the preambleof the packet including either the first structure or the secondstructure as the selected pattern. In some implementations, the firststructure can include a first number of instances of a sequence or itslogical complement, and the second structure can include a second numberof instances of the sequence or its logical complement. In some aspects,the first structure can include two instances of the sequence, and thesecond structure can include a single instance of the logical complementof the sequence. In addition, or in the alternative, the secondstructure can include one or more instances of a second sequence or oneof more instances of a logical complement of the second sequence, caninclude one or more instances of a pad sequence, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an example wireless system.

FIG. 2 shows a block diagram of an example wireless device.

FIG. 3 shows a block diagram of an example wake-up receiver.

FIG. 4A shows a graph depicting an example correlator output signalbased on a pattern contained in a preamble of a wake-up message.

FIG. 4B shows a graph depicting an example correlator output signalbased on a complemented pattern contained in a preamble of a wake-upmessage.

FIG. 5A shows a graph depicting an example correlator output signalbased on a short preamble of a wake-up message.

FIG. 5B shows a graph depicting an example correlator output signalbased on a long preamble of a wake-up message.

FIG. 5C shows a graph depicting an example correlator output signalbased on a first structure contained in the preamble of a wake-upmessage.

FIG. 5D shows a graph depicting an example correlator output signalbased on a second structure contained in the preamble of a wake-upmessage.

FIG. 6 shows a block diagram of an example aggregator.

FIG. 7A shows a graph depicting an example output waveform generated bythe aggregator of FIG. 6.

FIG. 7B shows a graph depicting another example output waveform based ona short pattern contained in a short preamble of a wake-up message.

FIG. 7C shows a graph depicting another example output waveform based ona long pattern contained in a long preamble of a wake-up message.

FIG. 8 shows a block diagram of another example aggregator.

FIG. 9 shows a graph depicting an example output waveform generated bythe aggregator of FIG. 8.

FIG. 10 shows an illustrative flow chart depicting an example operationfor determining a data rate of a received packet.

FIG. 11 shows an illustrative flow chart depicting another exampleoperation for determining a data rate of a received packet.

FIG. 12A shows an illustrative flow chart depicting an example operationfor indicating a data rate of a transmitted packet.

FIG. 12B shows an illustrative flow chart depicting another exampleoperation for indicating a data rate of a transmitted packet.

FIG. 12C shows an illustrative flow chart depicting an example operationfor selecting a pattern based on a data rate of a packet.

FIG. 13 shows an illustrative flow chart depicting another exampleoperation for indicating a data rate of a transmitted packet.

FIG. 14 shows a block diagram of an example pattern detector.

FIG. 15A shows a block diagram of an example long aggregator configuredto aggregate peaks in a correlator output signal for long patterns.

FIG. 15B shows a block diagram of an example short aggregator configuredto aggregate peaks in a correlator output signal for short patterns.

FIG. 16A shows a graph depicting an example output waveform generated bythe long aggregator of FIG. 15A.

FIG. 16B shows a graph depicting an example output waveform generated bythe short aggregator of FIG. 15B.

FIG. 17 shows an illustrative flow chart depicting another exampleoperation for indicating a data rate of a transmitted packet.

FIG. 18 shows an illustrative flow chart depicting another exampleoperation for determining a data rate of a received packet.

FIG. 19 shows a block diagram of another example pattern detector.

FIG. 20 shows a block diagram of another example aggregator.

FIG. 21A shows a graph depicting an example waveform based on acorrelation of a long pattern.

FIG. 21B shows a graph depicting an example waveform based on acorrelation of a short pattern.

FIG. 22 shows an illustrative flow chart depicting another exampleoperation for indicating a data rate of a transmitted packet.

FIG. 23 shows an illustrative flow chart depicting another exampleoperation for determining a data rate of a received packet.

FIG. 24 shows a table depicting example auto-correlation andcross-correlation metrics for a short pattern and a long pattern.

FIG. 25 shows an example wake-up receiver packet.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. The described implementations may be implemented in anydevice, system or network that is capable of transmitting and receivingRF signals according to any of the IEEE 802.11 specifications, or any ofthe IEEE 802.15 specifications, the Bluetooth® standard, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), Global System for Mobile communications(GSM), GSM/General Packet Radio Service (GPRS), Enhanced Data GSMEnvironment (EDGE), Terrestrial Trunked Radio (TETRA), Wideband-CDMA(W-CDMA), Evolution Data Optimized (EV-DO), 1×EV-DO, EV-DO Rev A, EV-DORev B, High Speed Packet Access (HSPA), High Speed Downlink PacketAccess (HSDPA), High Speed Uplink Packet Access (HSUPA), Evolved HighSpeed Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, or otherknown signals that are used to communicate within a wireless, cellularor internet of things (IOT) network, such as a system utilizing 3G, 4Gor 5G, or further implementations thereof, technology.

To conserve power, some wireless devices may include a primary radio forcommunicating data during an active power state and a low-power radiofor communicating data during a low-power state. To ensure that thewireless device receives all communications during the low-power state,the wireless device may periodically wake-up its low-power radio andlisten for messages (such as wake-up messages) from an access point (AP)indicating that communications are waiting to be transmitted to thewireless device. As part of the power conservation, communicationsassociated with the low-power radio may be transmitted at a lower datarate than communications associated with the primary radio.

Wake-up messages typically include a preamble, a signal field, and adata field. The preamble may be used for packet detection and symboltiming recovery, the signal field may indicate the data rate of thewake-up message, and the data field may contain data or instructions fora receiving device. Although the signal field may allow the receivingdevice to determine the data rate of the data field of the wake-upmessage, the signal field consumes overhead and increases the size andthe transmit duration of the wake-up message.

Implementations of the subject matter described in this disclosure mayallow a transmitting device to indicate the data rate of a wake-upmessage without using a signal field. In some implementations, thetransmitting device may embed a pattern into the preamble of the wake-upmessage to indicate the data rate at which the data field of the wake-upmessage is transmitted, for example, so that a receiving device candetermine the transmitted data rate by decoding and processing thepattern contained in the preamble of the wake-up message. In someaspects, the wake-up message includes a legacy preamble so that legacydevices can determine the data rate at which the data field of thewake-up message is transmitted without decoding any signaling fields(and without decoding any non-legacy portions of the wake-up message).

The transmitting device may select a data rate for transmitting the datafield of the wake-up message, and may select a pattern to embed withinthe preamble of the wake-up message based on the selected data rate. Insome implementations, the transmitting device may select a firststructure to use as the selected pattern if the selected data rate is alow data rate, and may select a second structure to use as the selectedpattern if the selected data rate is a high data rate (such that thefirst and second structures are different from each other). The firststructure may include a first number of instances of a sequence or itslogical complement, and the second structure may include a second numberof instances of the sequence or its logical complement. In some aspects,the first structure includes two instances of the sequence, and thesecond structure includes a single instance of the logical complement ofthe sequence. In addition, or in the alternative, the second structuremay include one or more instances of a second sequence or one of moreinstances of a logical complement of the second sequence, may includeone or more instances of a pad sequence, or both.

A receiving device may correlate the received pattern with a referencepattern to generate a correlator output signal, and may determine thedata rate of the data field of the wake-up message based on a presenceof one or more positive peaks or a presence of one or more negativepeaks in the correlator output signal. In some implementations, thepresence of one or more positive peaks in the correlator output signalmay correspond to the received pattern including two instances of thesequence, thereby indicating that the data field of the wake-up messagewas transmitted at the low date rate. Conversely, the presence of anegative peak in the correlator output signal may correspond to thereceived pattern including a single instance of the logical complementof the sequence, thereby indicating that the data field of the wake-upmessage was transmitted at the high date rate. In some aspects, the lowdata rate is approximately 62.5 kb/s, and the high data rate isapproximately 250 kb/s. In other aspects, one or both of the low datarate and the high data rate may be of other suitable values.

In other implementations, the transmitting device may embed a patterninto the preamble of the wake-up message to indicate a first data rate,and may embed a logical complement of the pattern into the preamble ofthe wake-up message to indicate a second data rate. A receiving devicemay correlate the received pattern with a reference pattern to generatea correlator output signal, and may determine the data rate based on apresence of a positive peak or a negative peak in the correlator outputsignal. In some aspects, detection of a positive peak in the correlatoroutput signal may indicate that the received pattern matches thereference pattern, which in turn may indicate that the wake-up messagewas transmitted at the first data rate. Detection of a negative peak inthe correlator output signal may indicate that the received pattern is alogical complement of the reference pattern (the received pattern is“logically complemented”), which in turn may indicate that the wake-upmessage was transmitted at the second data rate.

In some other implementations, the transmitting device may transmit awake-up message including a long preamble that contains a long patternto indicate the first data rate, and may transmit a wake-up messageincluding a short preamble that contains a short pattern to indicate thesecond data rate. A receiving device may correlate the received patternwith a reference pattern to generate a correlator output signal, and maydetermine the data rate based on a number of peaks present in thecorrelator output signal. In some aspects, detection of multiple peaksin the correlator output signal may indicate that the received patternis the long pattern, which in turn may indicate that the wake-up messagewas transmitted at the first data rate. Detection of a single peak inthe correlator output signal may indicate that the received pattern isthe short pattern, which in turn may indicate that the wake-up messagewas transmitted at the second data rate.

FIG. 1 shows a block diagram of an example wireless system 100. Thewireless system 100 is shown to include four wireless devices WD1-WD4, awireless access point (AP) 110, and a wireless local area network (WLAN)120. The WLAN 120 may be formed by a plurality of access points (APs)that may operate according to the IEEE 802.11 family of specifications(or according to other suitable wireless protocols). Thus, although onlyone AP 110 is shown in FIG. 1 for simplicity, it is to be understoodthat WLAN 120 may be formed by any number of access points such as theAP 110. The AP 110 may be assigned a unique MAC address that isprogrammed therein by, for example, the manufacturer of the accesspoint. Similarly, each of the wireless devices WD1-WD4 also may beassigned a unique MAC address.

In some implementations, the wireless system 100 may correspond to amultiple-input multiple-output (MIMO) wireless network, and may supportsingle-user MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO) communications.For other implementations, the wireless system 100 may correspond to orutilize orthogonal frequency division multiple access (OFDMA)communications. Further, although the WLAN 120 is depicted in FIG. 1 asan infrastructure Basic Service Set (BSS), in some otherimplementations, WLAN 120 may be an Independent Basic Service Set(IBSS), an Extended Service Set (ESS), an ad-hoc network, or apeer-to-peer (P2P) network (such as operating according to Wi-Fi Directprotocols). Thus, although not specifically shown in FIG. 1, in someimplementations the wireless devices WD1-WD4 may exchange signalsdirectly with each other (such as without the presence of the AP 110).

The wireless devices WD1-WD4 may be any suitable Wi-Fi enabled wirelessdevices including, for example, cell phones, IoT devices, personaldigital assistants (PDAs), tablet devices, laptop computers, or thelike. The wireless devices WD1-WD4 also may be referred to as a wirelessstation (STA), a user equipment (UE), a subscriber station, a mobileunit, a subscriber unit, a wireless unit, a remote unit, a mobiledevice, a wireless device, a wireless communications device, a remotedevice, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or some other suitable terminology. Insome implementations, each of the wireless devices WD1-WD4 may includeone or more transceivers, one or more processing resources (such asprocessors or ASICs), one or more memory resources, and a power source(such as a battery). The memory resources may include a non-transitorycomputer-readable medium (such as one or more nonvolatile memoryelements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) thatstores instructions for performing operations described with respect toFIGS. 10-11, FIGS. 12A-12C, FIG. 13, FIGS. 17-18, and FIGS. 22-23.

The AP 110 may be any suitable device that allows one or more wirelessdevices to connect to a network (such as a local area network (LAN),wide area network (WAN), metropolitan area network (MAN), or theInternet) via the AP 110 using Wi-Fi, Bluetooth, cellular, or any othersuitable wireless communication standards. In some implementations, theAP 110 may include one or more transceivers, a network interface, one ormore processing resources, and one or more memory sources. The memoryresources may include a non-transitory computer-readable medium (such asone or more nonvolatile memory elements, such as EPROM, EEPROM, Flashmemory, a hard drive, etc.) that stores instructions for performingoperations described with respect to FIGS. 10-11, FIGS. 12A-12C, FIG.13, FIGS. 17-18, and FIGS. 22-23. In some implementations, one or morefunctions of an AP, such as AP 110, may be performed by a wirelessstation, such as one of the wireless devices WD1-WD4 (for example, whenthe wireless station is operating as a soft AP).

The one or more transceivers in each of the wireless devices WD1-WD4 andthe AP 110 may include Wi-Fi transceivers, Bluetooth transceivers,cellular transceivers, or other suitable radio frequency (RF)transceivers (not shown for simplicity) to transmit and receive wirelesscommunication signals. Each transceiver may communicate with otherwireless devices in distinct frequency bands or using distinctcommunication protocols. For example, the Wi-Fi transceiver maycommunicate within a 2.4 GHz frequency band, within a 5 GHz frequencyband, or within a 60 GHz frequency band in accordance with the IEEE802.11 family of specifications. The cellular transceiver maycommunicate within various RF frequency bands in accordance with the LTEprotocol described by the 3rd Generation Partnership Project (3GPP)(such as between approximately 700 MHz and approximately 3.9 GHz) or inaccordance with other cellular protocols (such as the GSM protocol).

In some implementations, the transceivers included within the wirelessdevices WD1-WD4 also may include a wake-up receiver that can be used toreceive frames or packets when the wireless devices WD1-WD4 are in alow-power mode or state. In some aspects, the wake-up receiver in awireless device may listen for and receive a wake-up message transmittedfrom an AP, and may activate one or more Wi-Fi transceivers of thewireless device based on reception of the wake-up message.

FIG. 2 shows a block diagram of an example wireless device 200. Theexample wireless device 200 may be one implementation of at least one ofthe wireless devices WD1-WD4 or the AP 110 of FIG. 1. The wirelessdevice 200 may include one or more transceivers 210, a processor 220, amemory 230, and a number of antennas ANT1-ANTn. The transceivers 210 maybe coupled to antennas ANT1-ANTn, either directly or through an antennaselection circuit (not shown for simplicity). The transceivers 210 maybe used to transmit signals to and receive signals from other wirelessdevices including, for example, the AP 110 or one or more of thewireless devices WD1-WD4 of FIG. 1. Although not shown in FIG. 2 forsimplicity, the transceivers 210 may include any number of transmitchains to process and transmit signals to other wireless devices via theantennas ANT1-ANTn, and may include any number of receive chains toprocess signals received from the antennas ANT1-ANTn. Thus, the wirelessdevice 200 may be configured for MIMO operations. The MIMO operationsmay include SU-MIMO operations and MU-MIMO operations. In addition, thewireless device 200 may be configured for OFDMA communications and/orother suitable multiple access mechanisms, for example, as may beprovided in the IEEE 802.11ax standards.

In some implementations, the one or more transceivers 210 may include anumber of primary transceivers 211 and a number of wake-up receivers212. The primary transceivers 211 may be used for exchanging data withother wireless devices at relatively high data rates when the wirelessdevice 200 is in an active power mode, and the wake-up receiver 212 maybe used for receiving data when the wireless device 200 is in alow-power state (such as a power save state or a sleep state). Althoughthe wake-up receiver 212 may not support wideband transmissions and maynot be able to achieve the same data rates as the primary transceivers211, the wake-up receiver 212 consumes significantly less power than theprimary transceivers 211. During a low-power mode, the wireless device200 may reduce its power consumption (and thereby extend its batterylife) by de-activating or powering down the primary transceivers 211while using the wake-up receiver 212 to listen for messages (such aswake-up messages, beacon frames, and DTIMs) transmitted from an AP. Insome aspects, the wake-up receiver 212 may consume between 2 and 3orders of magnitude less power than the primary transceivers 211. Thewake-up receiver 212 may be separate from the primary transceivers 211,for example, by not sharing any components with the primary transceivers211. The separation between the primary transceivers 211 and the wake-upreceiver 212 may allow the wake-up receiver 212 to remain operationalwhen the primary transceivers 211 are in a low-power state.

The PHY layer of the wake-up receiver 212 may be configured foroperation in an unlicensed frequency spectrum, for example, to achievegreater bandwidth for a given power level without violating powerspectral density (PSD) limits. In addition, or in the alternative, thePHY layer of the wake-up receiver 212 may support a limited number ofdata rates (as compared to the PHY layers of the primary transceivers211) to minimize circuit complexity and area. For example, while the PHYlayers of the primary transceivers 211 may support as many as 20 (ormore) data rates for MIMO and OFDMA transmissions, the PHY layer of thewake-up receiver 212 may support only 2 data rates. In some aspects, thewake-up receiver 212 is a non-coherent receiver that operates on theenvelope (or amplitude) of received signals.

In some implementations, the wireless device 200 may use multipleantennas ANT1-ANTn to provide antenna diversity. Antenna diversity mayinclude polarization diversity, pattern diversity, and spatialdiversity. For purposes of discussion herein, the processor 220 is shownas coupled between the transceivers 210 and the memory 230. For actualimplementations, the transceivers 210, the processor 220, and the memory230 may be connected together using one or more buses (not shown forsimplicity).

The wireless device 200 may optionally include a display 221 andinput/output (I/O) components 222. The display 221 may be any suitabledisplay or screen allowing for user interaction and/or to present itemsor data to a user. In some aspects, the display 221 may be atouch-sensitive display. The I/O components 222 may be or include anysuitable mechanism, interface, or device to receive input (such ascommands) from the user and to provide output to the user. For example,the I/O components 222 may include (but are not limited to) a graphicaluser interface, keyboard, mouse, microphone and speakers, and so on.

In addition, or in the alternative, the wireless device 200 mayoptionally include or be coupled to one or more sensors 223 (such aswhen the wireless device 200 is an IoT device). The one or more sensors223 may be any suitable type of sensor that can detect or sense variousconditions near or related to the wireless device 200. For one examplein which the wireless device 200 is a component of a security system,the one or more sensors 223 may be configured to detect movement, todetect noise, to detect an opened window or door, and the like. Foranother example in which the wireless device 200 is a smart thermostat,the one or more sensors 223 may be configured to detect changes intemperature, to detect the presence or absence of persons in an area,and the like.

The memory 230 may include a database 231 that stores profileinformation for a plurality of wireless devices such as APs, wirelessstations, and IoT devices. The profile information for any given AP mayinclude, for example, the AP's service set identification (SSID), mediumaccess control (MAC) address, channel information, received signalstrength indicator (RSSI) values, goodput values, channel stateinformation (CSI), supported data rates, connection history with the AP,a trustworthiness value of the AP (e.g., indicating a level ofconfidence about the AP's location, etc.), and any other suitableinformation pertaining to or describing the operation of the AP. Theprofile information for a particular IoT device or wireless station mayinclude, for example, the device's MAC address, IP address, supporteddata rates, preferred frequency bands or channels, frequency hoppingschedules, a number of capabilities, and any other suitable informationpertaining to or describing the operation of the device.

The database 231 also may store a number of patterns that can be used toindicate various data rates of a packet, may store a number of referencepatterns derived from the selected patterns, and may store a mappingbetween each of the selected patterns and a corresponding data rate orpreamble length. In some implementations, the pattern contained in thepreamble of a received packet may be correlated with a reference patternto determine the data rate of the received packet. In addition, or inthe alternative, the length of a pattern contained in the preamble of areceived packet may be indicative of the received packet's data rate. Insome other implementations, the preamble length of a packet may beindicative of the packet's data rate.

The memory 230 also may include a non-transitory computer-readablestorage medium (such as one or more nonvolatile memory elements, such asEPROM, EEPROM, Flash memory, a hard drive, and so on) that may store thefollowing programs or instructions:

-   -   frame exchange instructions_232 to create and exchange frames        (such as data frames, control frames, management frames, and        trigger frames) and messages (such as data messages, paging        messages, wake-up messages, and so on) between the wireless        device 200 and other wireless devices, for example, as described        with respect to FIGS. 10-11, FIGS. 12A-12C, FIG. 13, FIGS.        17-18, and FIGS. 22-23;    -   pattern selection instructions_233 to select or generate a        pattern indicative of a selected data rate of a packet and to        embed the selected pattern within a preamble of the packet to be        transmitted to one or more other devices, for example, as        described with respect to FIGS. 10-11, FIGS. 12A-12C, FIG. 13,        FIGS. 17-18, and FIGS. 22-23;    -   reference pattern generation instructions 234 to select or        generate a reference pattern to be correlated with a pattern        contained in the preamble of a received packet, for example, as        described with respect to FIGS. 10-11, FIGS. 12A-12C, FIG. 13,        FIGS. 17-18, and FIGS. 22-23;    -   correlation instructions_235 to correlate a received pattern        with the reference pattern to generate a signal or waveform        indicative of a degree of correlation between the received        pattern and the reference pattern, for example, as described        with respect to FIGS. 10-11, FIGS. 12A-12C, FIG. 13, FIGS.        17-18, and FIGS. 22-23;    -   peak detection instructions_236 to detect a presence of one or        more positive peaks or one or more negative peaks in the signal        or waveform, for example, as described with respect to FIGS.        10-11, FIGS. 12A-12C, FIG. 13, FIGS. 17-18, and FIGS. 22-23; and    -   data rate determination instructions 237 to determine a data        rate of the received packet based on the detection of one or        more positive peaks or one or more negative peaks in the signal,        for example, as described with respect to FIGS. 10-11, FIGS.        12A-12C, FIG. 13, FIGS. 17-18, and FIGS. 22-23.

Execution of each set of instructions 232-237 by the processor 220 maycause the wireless device 200 to perform the corresponding functions.The non-transitory computer-readable medium of the memory 230 thusincludes instructions for performing all or a portion of the operationsdescribed with respect to FIGS. 10-11, FIGS. 12A-12C, FIG. 13, FIGS.17-18, and FIGS. 22-23.

The processor 220 may be any one or more suitable processors capable ofexecuting scripts or instructions of one or more software programsstored in wireless device 200 (such as within the memory 230). Theprocessor 220 may execute the frame exchange instructions 232 to createand exchange frames (such as data frames, control frames, managementframes, and trigger frames) and messages (such as data messages, pagingmessages, wake-up messages, and so on) between the wireless device 200and other wireless devices. In some implementations, the processor 220may execute the frame exchange instructions 232 to receive a wake-upmessage and to decode a pattern contained in the preamble of the wake-upmessage.

The processor 220 may execute the pattern selection instructions 233 toselect or generate a pattern indicative of a selected data rate of apacket (such as a wake-up message) to be transmitted to one or moreother devices and to embed the selected pattern within a preamble of thepacket. In some implementations, execution of the pattern selectioninstructions 233 may select the pattern to indicate a first data rate,and may select or generate a logical complement of the pattern toindicate a second data rate. In other implementations, execution of thepattern selection instructions 233 may select or generate a long patternto indicate the first data rate, and may select or generate a shortpattern to indicate the second data rate. As used herein, the term “longpattern” may refer to a pattern containing more than a number of bits ormore than a number of individual sequences, and the term “short pattern”may refer to a pattern containing less than the number of bits or lessthan the number individual sequences. In some other implementations,execution of the pattern selection instructions 233 may select orgenerate a first structure including a first number of instances of asequence or its logical complement to indicate a low data rate (such as62.5 kb/s), and may select or generate a second structure including asecond number of instances of the sequence or its logical complement toindicate a high data rate (such as 250 kb/s). In some aspects, the firststructure includes two instances of the sequence, and the secondstructure includes a single instance of the logical complement of thesequence. In addition, or in the alternative, the second structure alsomay include one or more instances of a second sequence or one or moreinstances of a logical complement of the second sequence, or one or moreinstances of a pad sequence, or both.

The processor 220 may execute the reference pattern generationinstructions 234 to select or generate a reference pattern to becorrelated with a pattern contained in the preamble of a receivedpacket. In some implementations, execution of the reference patterngeneration instructions 234 may select a stored pattern as the referencepattern. In other implementations, execution of the reference patterngeneration instructions 234 may generate the reference pattern based onthe stored pattern.

The processor 220 may execute the correlation instructions 235 tocorrelate the received pattern with the reference pattern to generate asignal indicative of a degree of correlation between the receivedpattern and the reference pattern. In some implementations, the signalmay include one or more large positive peaks or one or more largenegative peaks when the received pattern and the reference pattern arealigned in time (such as when all bits of the received pattern and thereference pattern match or when all bits of the received pattern arelogical complements to corresponding bits in the reference pattern), andthe signal may resemble noise when the received pattern and thereference pattern are not aligned in time (such as when the bits of thereceived pattern and the reference pattern do not match).

The processor 220 may execute the peak detection instructions 236 todetect a presence of one or more positive peaks or one or more negativepeaks in the signal or waveform. In some implementations, execution ofthe peak detection instructions 236 may determine whether a given spikeor peak in the signal or waveform qualifies as a large positive peak ora large negative peak, for example, using one or more threshold levels.Additionally or alternatively, execution of the peak detectioninstructions 236 may determine how many spikes or peaks appear in thesignal or waveform, may determine a spacing or time offset betweenspikes or peaks appearing in the signal or waveform, or a combinationthereof.

The processor 220 may execute the data rate determination instructions237 to determine a data rate of the received packet based on thedetection of one or more positive peaks or one or more negative peaks inthe signal or waveform. In some implementations, the detection of alarge positive peak or a large negative peak in the signal or waveformmay indicate whether the received packet contains a given pattern or alogical complement of the given pattern. In some aspects, a presence ofthe given pattern in the received packet may indicate that the packetwas transmitted at a first data rate, and a presence of the logicalcomplement of the given pattern in the received packet may indicate thatthe packet was transmitted at a second data rate. As used herein, theterm “large positive peak” may refer to a peak having a magnitude thatis more positive than a first value, and the term “large negative peak”may refer to a peak having a magnitude that is more negative than asecond value.

In other implementations, the detection of multiple large positive peaksor multiple large negative peaks in the signal may indicate whether thereceived packet includes a short preamble containing a short pattern orincludes a long preamble containing a long pattern. In some aspects, apresence of multiple large positive peaks or multiple large negativepeaks may indicate that the received packet includes a long pattern andwas transmitted at a low data rate, and a presence of a single largepositive peak or a single large negative peak may indicate that thereceived packet includes a short pattern and was transmitted at a highdata rate.

In some other implementations, the detection of one or more largepositive peaks in the signal may indicate that the packet wastransmitted using the low data rate, and the detection of a largenegative peak in the signal may indicate that the packet was transmittedusing the high data rate. In some aspects, a presence of multiple largepositive peaks in the signal may indicate that the received packetcontains the first structure including a first number of instances of asequence or its logical complement, and a presence of a large negativepeak in the signal may indicate that the received packet contains thesecond structure including a second number of instances of the sequenceor its logical complement.

Although functionality is described with respect to instructions232-237, in some implementations, an equivalent functionality may beprovided by hardware modules, firmware modules, or any feasiblecombination of hardware, firmware, and software modules (not shown inFIG. 2 for simplicity). In some implementations, one or more of thefunctions performed by executing the instructions 232-237 may beperformed by the wake-up receiver 212, for example, as described withrespect to FIG. 3.

The wake-up receiver 212 may consume significantly less power than theprimary transceivers 211, and may employ a different modulation schemethan the primary transceivers 211. A transmitting device may usemodulation to encode data onto a carrier signal by modifying one or morecharacteristics (such as the frequency, amplitude, and phase) of thecarrier signal, and a receiving device may use demodulation to decodedata modulated onto the carrier signal. A modulated waveform may bedivided into time units known as symbols. Each of the symbols may bemodulated separately, for example, by varying the phase and amplitude ofeach symbol. For example, a binary phase-shift keying (BPSK) modulationscheme conveys information by alternating between waveforms that aretransmitted with either no phase offset or with a 180° offset (such thateach symbol conveys a single bit of information). For another example, aquadrature amplitude modulation (QAM) modulation scheme uses two carriersignals, the in-phase signal component (I) and the quadrature signalcomponent (Q), to transmit data. The I signal component and the Q signalcomponent are transmitted with a phase offset of 90°, and each of the Iand Q signal components may be transmitted with a specific amplitudeselected from a finite set. The number of amplitude “bins” determinesthe number of bits that are conveyed by each symbol. For anotherexample, an ON-OFF keying (OOK) modulation scheme conveys information byeither transmitting a signal at a given amplitude (for the ON part ofthe signal) or transmitting the signal at a zero amplitude (for the OFFpart of the signal).

An AP (such as the AP 110 of FIG. 1) having queued data for delivery tothe wireless device 200 may transmit a wake-up message that causes thewireless device 200 to exit the low-power mode and enter an active powermode. The wake-up message may contain a pattern known to the wirelessdevice 200. The wake-up receiver 212 may receive the wake-up message,decode the pattern, and then wake-up (or activate) the primarytransceivers 211. Once activated, the primary transceivers 211 may beused to transmit and receive data at higher data rates (and usinggreater channel widths) than the wake-up receiver 212, therebyincreasing data throughput of the wireless device 200. Thereafter, whenthe primary transceivers 211 are no longer transmitting or receivingdata, the wireless device 200 may return to the low-power state andpower-down various components of the primary transceivers 211 toconserve power.

In some implementations, one or more portions of the wake-up message maybe encoded using an OOK modulation scheme. In some aspects, the wake-upmessage may be transmitted using a single carrier signal, and thepattern may be encoded onto the carrier signal using a binary OOKmodulation scheme. In other aspects, the wake-up message may betransmitted using a multi-tone carrier signal, and the device specificpattern may be encoded onto the multi-tone carrier signal using an OOKmodulation scheme.

A conventional wake-up message typically includes a preamble, a signalfield, and a data field. The preamble may be used for packet detectionand symbol timing recovery, the signal field may indicate the data rateof the wake-up message, and the data field may contain data orinstructions for the wireless device 200. Although the signal field mayallow a receiving device (such as the wireless device 200) to determinethe data rate of the data field, the signal field consumes overhead andincreases the size and the transmit duration of the wake-up message.Eliminating the signal field may reduce the overhead of the wake-upmessage and thereby decrease the transmit duration of the wake-upmessage.

In accordance with aspects of the present disclosure, a wake-up messageis disclosed that includes a preamble and a data field, but not a signalfield, to reduce the overhead of the wake-up message. The elimination ofthe signal field may reduce the overhead (and thus the transmitduration) of the wake-up message. In some implementations, an indicationof the data rate of the data field of the wake-up message may be encodedwithin a pattern contained in the preamble of the wake-up message. Morespecifically, a transmitting device may embed, in the preamble of thewake-up message, a special pattern that indicates the data rate of thedata field of the wake-up message. The pattern also may indicate alength of the wake-up message's preamble. A receiving device may decodethe special pattern contained in the preamble of the wake-up message,and determine the data rate of the data field (and also the preamblelength) of the wake-up message based on the decoded special pattern.

FIG. 3 shows a block diagram of an example wake-up receiver 300. Thewake-up receiver 300, which may be one implementation of the wake-upreceiver 212 of FIG. 2, may determine the data rate of a receivedwake-up message 390 based at least in part on a correlation between thepattern contained in the received wake-up message 390 and a knownreference pattern. In some implementations, the wake-up receiver 300 maydetermine the data rate of the wake-up message 390 based on whether thereceived pattern is the reference pattern or is a logically complementedversion of the reference pattern. In other implementations, the wake-upreceiver 300 may determine the data rate of the wake-up message 390based on whether the wake-up message 390 includes a short preamblecontaining a short pattern or includes a long preamble containing a longpattern. In some other implementations, the wake-up receiver 300 maydetermine the data rate of the wake-up message 390 based on whether thepreamble of the wake-up message 390 contains the first structure or thesecond structure (such as either the pattern W or the pattern [W, W]. Inthis manner, the receiving device may determine the data rates ofwake-up messages 390 that do not include a signal field.

The wake-up receiver 300 is shown to include an analog front-end (AFE)310, a baseband processor 320, a correlator 330, a peak detector 340, areference signal generator 350, and a memory 360. The AFE 310 mayinclude any suitable circuits or components capable of receivingmessages or packets in the form of signals and down-converting thereceived signals from a carrier frequency to a baseband frequency. Thebaseband processor 320 may be any suitable processor capable ofprocessing baseband signals. In some aspects, the AFE 310 and thebaseband processor 320 may be configured for narrowband communications(such as wireless transmissions having a relatively narrow bandwidth of,for example, 4 MHz).

The correlator 330 includes a first input coupled to an output of thebaseband processor 320, a second input coupled to an output of thereference signal generator 350, and an output coupled to an input of thepeak detector 340. The correlator 330 may be configured to correlate areceived pattern contained in the preamble of the wake-up message with areference pattern provided by the reference signal generator 350 togenerate a correlator output signal. The correlator output signal isprovided to the peak detector 340. The use of a single correlator 330 inthe wake-up receiver 300 may not only reduce power consumption but alsoconserve circuit area, for example, as compared with using a firstcorrelator to detect short preambles and a second correlator to detectlong preambles.

The peak detector 340 may detect a presence of positive peaks or apresence of negative peaks in the correlator output signal. The peakdetector 340 may use a number of threshold levels to determine whether aparticular spike in the correlator output signal qualifies as either apositive peak or a negative peak. In some implementations, the detectionof a positive peak in the correlator output signal may indicate that thepacket was transmitted at a first data rate, and the detection of anegative peak in the correlator output signal may indicate that thepacket was transmitted at a second data rate. In other implementations,the detection of a long preamble may indicate that the packet wastransmitted at the first data rate, and the detection of a shortpreamble may indicate that the packet was transmitted at the second datarate. In some other implementations, a presence of the first structurein the packet preamble may indicate that the data field of the packetwas transmitted at the first data rate, and a presence of the secondstructure in the packet preamble may indicate that the data field of thepacket was transmitted at the second data rate. The first data rate maybe one of a low data rate and a high data rate, and the second data ratemay be the other of the low data rate and the high data rate. In someaspects, the low data rate is 62.5 kb/s, and the high data rate is 250kb/s.

The memory 360 may store the same pattern used by the transmittingdevice (not shown for simplicity). In some implementations, the patternmay be device-specific, for example, so that the wake-up receiver 300can determine that a packet containing the device-specific pattern isintended for the wireless device 200. In such implementations, thetransmitting device may store a plurality of different patterns to beused for transmitting packets (such as the wake-up message 390) to aplurality of different receiving devices. In other implementations, thepattern may be a sequence (or a number of sequences) provided by theIEEE 802.11ba specification, for example, so that all transmittingdevices use the specified pattern and all receiving devices store thespecified pattern for use as the reference pattern.

The reference signal generator 350 provides a reference pattern to thecorrelator 330. In some implementations, the reference signal generator350 may forward the pattern stored in the memory 360 as the referencepattern to the correlator 330. In other implementations, the referencesignal generator 350 may generate the reference pattern based on thepattern stored in the memory 360. In some aspects, the reference signalgenerator 350 may generate a reference pattern R from a stored sequenceS using the expression R=(2×S)−1, for example, so that 1's in the storedsequence S appear as 1's in the reference pattern R, and 0's in thestored sequence S appear as −1's bits in the reference pattern R. Inaddition, or in the alternative, the reference pattern R may be zeromean (such that it includes equal numbers of 1's and −1's), which inturn may cause the correlator output signal to also be zero mean.

A transmitting device may use wake-up messages as disclosed herein tosend data or instructions to a receiving device (such as the wirelessdevice 200 of FIG. 2) as follows. The transmitting device may select apattern that is known to the receiving device, may embed the selectedpattern into the preamble of a wake-up message 390, and may transmit thewake-up message 390 to the receiving device. In some implementations,the transmitting device may select a maximum length sequence (MLS) asthe pattern to embed in the preamble of the wake-up message 390.

A MLS is a sequence having specific correlation properties such thatwhen a MLS is correlated with a copy of itself, the resulting correlatoroutput signal may include a large peak (such as a particular peak thatis distinguishable from other peaks in the correlator output signal)when the MLS and its copy are aligned in time, and may resemble noisewhen the MLS and its copy are not aligned in time. For example, when theMLS and its copy are aligned in time so that the bits of the MLS matchcorresponding bits of its copy, the matching 1's in the MLS and its copyproduce a large positive peak in the correlator output signal.Similarly, when the MLS and a logical complement of the MLS are alignedin time, the result is a large negative peak in the correlator outputsignal. Conversely, when the MLS and its copy or its logical complementare not aligned in time, the resulting correlator output signal includesneither a large positive peak nor a large negative peak, but ratherresembles noise. These correlation properties render MLSs well-suitedfor symbol timing recovery using the methods described herein.

In some implementations, the transmitting device selects an MLS as thepattern, and then embeds either the MLS or its logical complement intothe preamble of the wake-up message 390. The MLS is denoted herein as asequence S, and may be used to indicate a first data rate of the wake-upmessage 390. The logical complement of the MLS is denoted herein as acomplemented sequence S, and may be used to indicate a second data rateof the wake-up message 390. In some aspects, the transmitting device mayuse the sequence S to indicate the low data rate of 62.5 kb/s, and mayuse the complemented sequence S to indicate the high data rate of 250kb/s. In other aspects, the transmitting device may use the complementedsequence S to indicate the low data rate of 62.5 kb/s, and may use thesequence S to indicate the high data rate of 250 kb/s.

In other implementations, the transmitting device may select the datarate at which the data field of the wake-up message is to betransmitted, may select a first structure to embed as the selectedpattern within the wake-up message's preamble if the selected data rateis a low data rate, and may select a second structure to embed as theselected pattern within the wake-up message's preamble if the selecteddata rate is a high data rate. In some implementations, the firststructure may be longer than the second structure. In some aspects, thefirst structure may include a first number of instances of a sequence orits logical complement, and the second structure may include a secondnumber of instances of the sequence or its logical complement. In someimplementations, the first structure includes two instances of asequence W, and the second structure includes a single instance of thelogical complement of the sequence (denoted herein as W). The firststructure may be formed by the concatenation of two copies of thesequence W, and may be denoted herein as [W, W]. In some aspects, thesequence W=[10100100101110110001011100111000], and the logicallycomplemented sequence W=[01011011010001001110100011000111].

In some implementations, the transmitting device may transmit theselected pattern (such as the sequence S, the complemented sequence S,the first structure, the second structure, and so on) using OOKmodulation of a single carrier signal, for example, by selectivelyturning on and off the carrier signal on a per-symbol basis. In otherimplementations, the transmitting device may transmit the selectedpattern using multi-carrier OOK modulation of an OFDM waveform. Forexample, the transmitting device may transmit a logic 1 by modulatingthe carrier signal, and may transmit a logic 0 by not modulating thecarrier signal. In this manner, the transmitting device may transmit thepattern by multiplying an OFDM waveform by sequential bits in thepattern. Using OOK modulation of an OFDM waveform to transmit logic 1and logic 0 bits may allow the transmitting device to increase thetransmission bandwidth of the wake-up message without increasing thedata rate.

The wake-up receiver 300 in the receiving device receives the wake-upmessage 390, down-converts the wake-up message 390 using the AFE 310,and extracts the pattern contained in the preamble. The received patternand the reference pattern are provided to the correlator 330, whichcorrelates the received pattern and the reference pattern to generatethe correlator output signal.

In implementations for which the preamble of the wake-up message 390contains the sequence S, the correlator output signal generated by thecorrelator 330 may include a large positive peak if the receivedsequence S is aligned in time with the reference pattern R (such thatthe received sequence S “matches” the reference pattern R). The largepositive peak appears in the correlator output signal because all the1's in the received sequence S are multiplied by corresponding 1's inthe reference pattern R, and all the 0's in the received sequence S aremultiplied by corresponding −1's in the reference pattern R. Conversely,if the received sequence S is not aligned in time with the referencepattern R (such that the received sequence S does not “match” thereference pattern R), then the correlator output signal may be anear-zero waveform (resembling noise) due to the correlation propertiesof the MLS.

In implementations for which the preamble of the wake-up message 390contains the complemented sequence S, the correlator output signal mayinclude a large negative peak if the received complemented sequence S isaligned in time with the reference pattern R (such that the receivedcomplemented sequence S “matches” the reference pattern R). The largenegative peak appears in the correlator output signal because all the0's in the received complemented sequence S are multiplied bycorresponding 1's in the reference pattern R, and all the 1's in thereceived complemented sequence S are multiplied by corresponding −1's inthe reference pattern R. Conversely, if the received complementedsequence S is not aligned in time with the reference pattern R (suchthat the received complemented sequence S does not “match” the referencepattern R), then the correlator output signal may be a near-zerowaveform (resembling noise) due to the correlation properties of thecomplemented MLS.

Because the transmitting device uses complementary MLSs embedded in thepreamble of the wake-up message 390 to indicate its data rate, thewake-up receiver 300 may determine the data rate of the received wake-upmessage 390 by determining whether the preamble of the wake-up message390 contains the sequence S or the complemented sequence S. For example,if the correlator output signal includes a large positive peak (such asdepicted in FIG. 4A), then the wake-up receiver 300 may determine thatthe wake-up message 390 contains the sequence S and was transmitted atthe first data rate. Conversely, if the correlator output signalincludes a large negative peak (such as depicted in FIG. 4B), then thewake-up receiver 300 may determine that the wake-up message 390 containsthe complemented sequence S and was transmitted at the second data rate.In this manner, the wake-up receiver 300 may determine the data rate ofthe data field in the wake-up message 390 without the presence of adedicated signal field in the wake-up message 390.

In implementations for which the preamble of the wake-up message 390contains the first structure including two instances of the sequence W,the correlator output signal generated by the correlator 330 may includetwo large positive peaks if the two instances of the sequence W arealigned in time with the reference pattern R (such that the receivedpattern “matches” the reference pattern R). A large positive peak mayappear in the correlator output signal because all the 0's in a receivedinstance of the sequence W are multiplied by corresponding −1's in thereference pattern R, and all the 1's in the received instance of thesequence W are multiplied by corresponding 1's in the reference patternR. Conversely, if the two instances of the sequence W are not aligned intime with the reference pattern R (such that the received pattern doesnot “match” the reference pattern R), then the correlator output signalmay be a near-zero waveform (resembling noise) due to the correlationproperties of the sequence W.

In implementations for which the preamble of the wake-up message 390contains the second structure including a single instance of thelogically complemented sequence W, the correlator output signalgenerated by the correlator 330 may include a large negative peak if thereceived complemented sequence W is aligned in time with the referencepattern R (such that the received pattern “matches” the referencepattern R). The large negative peak may appear in the correlator outputsignal because all the 0's in the received complemented sequence W aremultiplied by corresponding 1's in the reference pattern R, and all the1's in the received complemented sequence W are multiplied bycorresponding −1's in the reference pattern R. Conversely, if thereceived complemented sequence W is not aligned in time with thereference pattern R (such that the received pattern does not “match” thereference pattern R), then the correlator output signal may be anear-zero waveform (resembling noise) due to the correlation propertiesof the received complemented sequence W.

FIG. 4A shows a graph 400 depicting an example correlator output signal402 based on the sequence S contained in the preamble of the wake-upmessage 390. The correlator output signal 402 is generated by thecorrelator 330 when the received sequence S is aligned in time with thereference pattern R, and thus includes a large positive peak 404. Notethat the correlator output signal 402 is one-half the length of thereceived sequence S. For example, if the received sequence S is 32 bitslong, then the correlator output signal 402 is 16 bits long.

FIG. 4B shows a graph 410 depicting an example correlator output signal412 based on the complemented sequence S contained in the preamble ofthe wake-up message 390. The correlator output signal 412 is generatedby the correlator 330 when the received complemented sequence S isaligned in time with the reference pattern R, and thus includes a largenegative peak 414.

Referring again to FIG. 3, the receiving device may use a singlecorrelator (such as the correlator 330) to determine whether thereceived packet includes the sequence S or the complemented sequence S,and therefore to determine whether the wake-up message 390 wastransmitted at the low data rate or the high data rate. Because thelength of the sequence S contained in the preamble of the wake-upmessage 390 is based on the low data rate, the preamble of the wake-upmessage 390 is the same length for both the low data rate and the highdata rate, even though a short preamble could be used when transmittingthe wake-up message 390 at the high data rate. As a result, the wake-upmessage 390 may include unnecessary overhead when transmitted at thehigh data rate.

In some other implementations, the transmitting device may use a shortpreamble when transmitting the wake-up message 390 at the high datarate, and may use a long preamble when transmitting the wake-up message390 at the low data rate. Generally, communications at lower data ratesrequire longer preambles than communications at higher data ratesbecause of the lower SNR associated with the lower data ratecommunications. In some implementations, the short preamble may be of alength suitable for use with the high data rate, and may contain a shortpattern including one instance or copy of the sequence S (oralternatively one instance of the complemented sequence S). In someimplementations, the long preamble may be of a length suitable for usewith the low data rate, and may include multiple instances or copies ofthe sequence S, the complemented sequence S, or both. In some aspects inwhich the low data rate is 62.5 kb/s and the high data rate is 250 kb/s,the long pattern includes four total instances of the sequence S or itscomplement S because the high data rate is four times the low data rate(250/62.5=4), and thus requires a preamble that is approximately fourtimes as long as the short preamble. In this manner, the transmittingdevice may use a short preamble containing a short pattern (such as the32-bit sequence S described above) when transmitting a wake-up messageat the high data rate, and may use a long preamble containing a longpattern (such as four copies of the sequence S and/or the complementedsequence S) when transmitting a wake-up message at the low data rate.Thus, in some aspects, the short preamble contains a 32-bit pattern, andthe long preamble contains a 128-bit pattern. If the preamble bitduration is 1 μs, then the short preamble has a duration of 32 μs, andthe long preamble has a duration of 128 μs.

The long pattern may be generally expressed as:[S·B ₁ ,S·B ₂ ,S·B ₃ , . . . S·B _(N)]where the operation S·B indicates a bit-by-bit exclusive-OR (XOR)operation between the sequence S and a bitstring or bitmap B denotingwhether the corresponding sequence is logically complemented or not. Asused herein, when B=0, the operation S·B produces the original sequenceS, and when B=1, the operation S·B produces the complemented sequence S.For example, a long pattern containing four copies of the complementedsequence S may be denoted as [S, S, S, S ] or expressed by a bitmapB=1111. For another example, a long pattern containing a concatenationof the complemented sequence S, two copies of the sequence S, followedby the complemented sequence S may be denoted as [S, S, S, S ] orexpressed by a bitmap B=1001. For another example, a long patterncontaining a concatenation of two copies of the complemented sequence S,followed by the sequence S, and followed by the complemented sequence Smay be denoted as [S, S, S, S ] or expressed by a bitmap B=1101.

Thus, in accordance with aspects of the present disclosure, thetransmitting device may select a short preamble containing a shortpattern (such as including one instance of the sequence S or oneinstance of the complemented sequence S) when transmitting a wake-upmessage at the high data rate, and may select a long preamble containinga long pattern (such as including multiple instances of the sequence Sand/or the complemented sequence S) when transmitting the wake-upmessage at the low data rate. Both the short pattern and the longpattern may be constructed to allow the receiving device to performpacket detection, to perform symbol timing recovery, and to determinewhether the wake-up message includes a short preamble or a longpreamble. In this manner, the receiving device may determine the datarate of the wake-up message based on the length or duration of itspreamble. For example, a determination that the wake-up message includesa long preamble (such as 128 bits) may indicate that the wake-up messagewas transmitted at the low data rate, and a determination that thewake-up message includes a short preamble (such as 32 bits) may indicatethat the wake-up message was transmitted at the high data rate.

In addition, because both the short preamble and the long preamble areconstructed using one or more copies of a MLS or a logical complement ofthe MLS, the receiving device may use a single correlator to determinewhether the received packet includes a short preamble or a longpreamble. The use of a single correlator that can detect both a shortpreamble and a long preamble may not only reduce power consumption butalso may conserve circuit area, for example, as compared with usingdifferent correlators to detect short preambles and long preambles.

Referring again to FIG. 3, the transmitting device may indicate the highdata rate by embedding a single copy of the sequence S (or alternativelya single copy of the complemented sequence S) into a short preamble ofthe wake-up message 390. The wake-up receiver 300 in the receivingdevice receives the wake-up message 390, down-converts the wake-upmessage 390 using the AFE 310, and extracts the sequence S contained inthe short preamble. The received sequence S and the reference pattern R(which may be derived from either the sequence S or the complementedsequence S) are provided to the correlator 330, which correlates thereceived sequence S and the reference pattern R to generate thecorrelator output signal.

When the short preamble of the wake-up message 390 contains the sequenceS, the correlator output signal may include a large positive peak if thereceived sequence S is aligned in time with the reference pattern R(when the reference pattern R=2S−1), for example, as depicted in FIG.5A. The large positive peak appears in the correlator output signalbecause all the 1's in the received sequence S are multiplied bycorresponding 1's in the reference pattern R, and all the 0's in thereceived sequence S are multiplied by corresponding −1's in thereference pattern R. Conversely, if the received short pattern is notaligned in time with the reference pattern R, then the correlator 330generates a correlator output signal having near-zero waveform due tothe correlation properties of the MLS-based sequence S.

In some other implementations, the short preamble of the wake-up message390 may contain the complemented sequence S (rather than the sequenceS). If the received complemented sequence S is aligned in time with thereference pattern R (such as when the reference pattern R=2S−1), thecorrelator output signal may include a large negative peak, for example,as depicted in FIG. 4B. The large negative peak appears in thecorrelator output signal because all the 0's in the complementedsequence S are multiplied by corresponding 1's in the reference patternR, and all the 1's in the received complemented sequence S aremultiplied by corresponding −1's in the reference pattern R. Conversely,if the received complemented sequence S is not aligned in time with thereference pattern R, then the correlator 330 generates a correlatoroutput signal having near-zero waveform due to the correlationproperties of the MLS-based complemented sequence S.

FIG. 5A shows a graph 500 depicting an example correlator output signal502 based on the wake-up message 390 including a short preamblecontaining the sequence S. The correlator output signal 502 is generatedby the correlator 330 when the short sequence S is aligned in time withthe reference pattern R=2S−1, and thus includes a large positive peak504. Note that the correlator output signal 502 is one-half the lengthof the received sequence S. For example, if the received sequence S is32 bits long, then the correlator output signal 502 is 16 bits long.

Referring again to FIG. 3, the transmitting device may indicate the lowdata rate by embedding a long pattern into a long preamble of thewake-up message 390. The long pattern may contain four instances of thesequence S and/or the complemented sequence S. For example, the longpattern contained in the wake-up message 390 may be formed by theconcatenation of four copies of the complemented sequence S, andtherefore may be denoted as [S, S, S, S]. The wake-up receiver 300 inthe receiving device receives the wake-up message 390, down-converts thewake-up message 390 using the AFE 310, and extracts the long pattern [S,S, S, S]. The correlator 330 correlates the long pattern [S, S, S, S]with the reference pattern R to generate the correlator output signal.

Because the long pattern contains four copies of the complementedsequence S, the correlator output signal may include four large negativepeaks if the long pattern is aligned in time with the reference patternR (because the reference pattern R=2S−1), for example, as depicted inFIG. 5B. Each of the four large negative peaks appears in the correlatoroutput signal because all the 0's in the received complemented sequenceS are multiplied by corresponding 1's in the reference pattern R, andall the 1's in the received complemented sequence S are multiplied bycorresponding −1's in the reference pattern R. Conversely, if thereceived long pattern is not aligned in time with the reference patternR, then the correlator 330 generates a correlator output signal havingnear-zero waveform due to the correlation properties of the MLS-basedlong pattern.

FIG. 5B shows a graph 510 depicting an example correlator output signal512 based on the wake-up message 390 having a long preamble containingfour copies of the complemented sequence S. The correlator output signal512 is generated by the correlator 330 when the received long pattern isaligned in time with the reference pattern R and thus includes fourlarge negative peaks 514.

Thus, in some aspects, the peak detector 340 may determine whether areceived wake-up message includes a short preamble or a long preamblebased on the number of peaks detected in the correlator signal. Forexample, a detection of one peak in the correlator output signal (suchas the positive peak 504 in the graph 500 of FIG. 5A) may indicate ashort preamble and therefore also may indicate that the wake-up messagewas transmitted using the high data rate. A detection of four peaks inthe correlator output signal (such as the four negative peaks 514 in thegraph 510 of FIG. 5B) may indicate a long preamble and therefore alsomay indicate the wake-up message was transmitted using the low data rate

Referring again to FIG. 5B, the long preamble containing the longpattern is used for low data rate communications. In some instances, thefour negative peaks 514 in the correlator output signal 512 may not beof sufficient amplitude to be reliably detected in the presence of a lowSNR. The wake-up receiver's ability to detect peaks in the correlatoroutput signal for the long preamble may be improved by combining oraggregating the four peaks 514 in the correlator output signal 512.Thus, in some implementations, an aggregator may be provided within thewake-up receiver 300 to aggregate multiple peaks in the correlatoroutput signal which correspond to the correlation of multiple copies orinstances of the sequence S and/or the complemented sequence S.

FIG. 5C shows a graph 520 depicting an example correlator output signal522 based on the wake-up message 390 containing a first structureincluding the two instances of the sequence W. In some implementations,transmitting device may indicate the low data rate by embedding thefirst structure [W, W] as the selected pattern into the preamble of thewake-up message 390. For purposes of discussion herein, the correlatoroutput signal 522 may be generated by the correlator 330 of FIG. 3. Inother implementations, the correlator output signal 522 may be generatedby another suitable correlator circuit.

The correlator output signal 522 may include two large positive peaks524A and 524B when the received structure [W, W] is aligned in time withthe reference pattern R. Each of the two large positive peaks 524A and524B may appear in the correlator output signal 522 because all the 0'sin the received structure [W, W] are multiplied by corresponding −1's inthe reference pattern R, and all the 1's in the received structure [W,W] are multiplied by corresponding 1's in the reference pattern R.Conversely, if the received structure [W, W] is not aligned in time withthe reference pattern R, then the correlator output signal may have anear-zero waveform (such as because of the correlation properties of thefirst structure).

Referring also to FIG. 3, the wake-up receiver 300 in the receivingdevice may receive the wake-up message 390, may down-convert the wake-upmessage 390 using the AFE 310, and nay extract the first structure [W,W]. The correlator 330 in the receiving device may correlate the firststructure [W, W] with the reference pattern R to generate the correlatoroutput signal 522 of FIG. 5C.

FIG. 5D shows a graph 530 depicting an example correlator output signal532 based on the wake-up message 390 containing a second structureincluding a single instance of the logically complemented sequence W. Insome implementations, transmitting device may indicate the high datarate by embedding the second structure W as the selected pattern intothe preamble of the wake-up message 390. For purposes of discussionherein, the correlator output signal 532 may be generated by thecorrelator 330 of FIG. 3. In other implementations, the correlatoroutput signal 532 may be generated by another suitable correlatorcircuit.

The correlator output signal 532 may include a large negative peak 534when the received structure W is aligned in time with the referencepattern R. The large negative peak 534 may appear in the correlatoroutput signal 532 because all the 0's in the received structure W aremultiplied by corresponding 1's in the reference pattern R, and all the1's in the received structure W are multiplied by corresponding −1's inthe reference pattern R. Conversely, if the received structure W is notaligned in time with the reference pattern R, then the correlator outputsignal may have a near-zero waveform (such as because of the correlationproperties of the second structure).

Referring also to FIG. 3, the wake-up receiver 300 in the receivingdevice may receive the wake-up message 390, may down-convert the wake-upmessage 390 using the AFE 310, and may extract the second structure W.The correlator 330 in the receiving device may correlate the secondstructure W with the reference pattern R to generate the correlatoroutput signal 532 of FIG. 5D.

FIG. 6 shows a block diagram of an example aggregator 600. Theaggregator 600 includes an input to receive a correlator output signal(CS₀), an output to generate an aggregator output signal, a number ofseries-connected delay elements 610(1)-610(3), and a summer 620. In someimplementations, the aggregator 600 may be provided between thecorrelator 330 and the peak detector 340 of the wake-up receiver 300 ofFIG. 3, for example, so that the output of the correlator 330 is coupledto the input of the first delay element 610(1) and the output of thesummer 620 is coupled to the input of the peak detector 340. Each of thedelay elements 610(1)-610(3) may be configured to delay the correlatoroutput signal by a duration of the sequence S. For example, the firstdelay element 610(1) delays the correlator output signal CS₀ provided bythe correlator 330 to generate a first delayed correlator signal CS₁,the second delay element 610(2) delays the first delayed signal CS₁ togenerate a second delayed correlator signal CS₂, and the third delayelement 610(3) delays the second delayed signal CS₂ to generate a thirddelayed correlator signal CS₃. In some aspects, each of the delayelements 610(1)-610(3) may introduce a delay of 32 μs.

The summer 620 includes inputs coupled to the output of the correlator330 and to an output of each of the delay elements 610(1)-610(3). Thesummer 620 sums (or aggregates) the correlator output signal CS₀ and thethree delayed correlator signals CS₁-CS₃ to generate an aggregatoroutput signal in which the peaks of the correlator output signal CS₀ areadded together, for example, as depicted in FIG. 7A.

FIG. 7A shows a graph 700 depicting an example output waveform 702generated by the aggregator of FIG. 6. The output waveform 702 is shownto include a large negative peak 704 that represents the sum of the fournegative peaks 514 in the graph 510 of FIG. 5B. Note that the outputwaveform 702 also includes smaller negative peaks 706-708 whichrepresent sums of less than all four negative peaks 514. For example,the negative peak 706 may represent the sum of three of the negativepeaks 514, the negative peak 707 may represent the sum of two of thenegative peaks 514, and the negative peak 708 may represent one of thenegative peaks 514.

Because of the low SNR of the low data rate, the negative peak 706 maybe strong enough to be incorrectly detected by the peak detector. Theundesirable effects associated with the smaller negative peaks 706-708may be corrected by using a different long pattern. In some aspects, thetransmitting device may use a long pattern including at least oneinstance of the sequence S and at least one instance of the sequence S,rather than a long pattern that consists of only copies of S or onlycopies of S, to reduce incorrect peak detections. For example, the longpattern [S, S, S, S] may be used instead of the long pattern [S, S, S,S].

FIG. 7B shows a graph 710 depicting an example output waveform 712generated by the correlator 330 based on the short pattern containingone instance of the sequence S. The output waveform 712 includes a largepositive peak 714. FIG. 7C shows a graph 720 depicting an example outputwaveform 722 generated by the correlator 330 based on the long pattern[S, S, S, S]. The output waveform 722 includes a large positive peak 724corresponding to the one instance of the sequence S and three largenegative peaks 726 corresponding to the three instances of S.

FIG. 8 shows a block diagram of another example aggregator 800. Theaggregator 800 is similar to the aggregator 600 of FIG. 6, except that alogic element 810 is provided between the output of the first delayelement 610(1) and the corresponding input of the summer 620. The logicelement 810 multiplies the delayed signal CS₁ by −1, for example, toaccount for the positive peak caused by the one instance of the sequenceS in the long pattern of [S, S, S, S].

In some other implementations, other long patterns may be used by thetransmitting device, and the logic element 810 may be used to multiplyany combination of the correlator signals CS₁-CS₃ provided by therespective delay elements 610(1)-610(3).

FIG. 9 shows a graph 900 depicting an example output waveform 902generated by the aggregator 800 of FIG. 8. The output waveform 902,which is generated by the aggregator 800 based on the long pattern of[S, S, S, S], is shown to include a large negative peak 904 withsignificantly reduced side peaks as compared with the output waveform702 of FIG. 7A.

In some other implementations, a transmitting device may use twodifferent sequences to construct the short preamble and the longpreamble. In some aspects, the first sequence S₀ is a MLS, and thesecond sequence S₁ is orthogonal to the first sequence S₀, for example,such that a bitwise exclusive-OR operation on the first sequence S₀ andthe second sequence S₁ generates a resulting sequence for which thenumber of 1's is approximately equal to one-half the number of bits ineach of the first and second sequences. The concatenation of the firstand second sequences may be expressed as [S₀·B₁, S₁·B₂, S₁·B₃, . . .S₀·B_(N)], where the operation S·B indicates a bit-by-bit exclusive-ORoperation between a given one of the sequences S₀ and S₁ and a bitstringB. In other words, while each bit of the complemented sequence S is thelogical opposite of a corresponding bit of the original sequence S, eachbit of the second sequence S₁ may or may not be the logical opposite ofa corresponding bit of the first sequence S₀—as long as the aperiodiccorrelation between the first sequence S₀ and the second sequence S₁tends to be zero (but not necessarily zero).

FIG. 10 shows an illustrative flow chart depicting an example operation1000 for determining a data rate of a received packet. The exampleoperation 1000 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thereceiving device receives, from the transmitting device, a patterncontained in a preamble of the packet (1002). The receiving devicegenerates a waveform based on a correlation between the received patternand a reference pattern (1004). In some implementations, the patterncomprises one or more instances of a maximal length sequence (MLS), andthe reference pattern comprises one or more instances of the MLS or avariant of the MLS (such as a logical complement of the MLS). In someaspects, the reference pattern is derived from the MLS by converting the0's of the MLS to −1's, and maintaining the 1's of the MLS.

The receiving device determines the data rate of the packet to be afirst data rate based on a presence of a large positive peak in thewaveform (1006), and determines the data rate of the packet to be asecond data rate based on a presence of a large negative peak in thewaveform (1008). In some implementations, the receiving device comprisesa non-coherent wake-up receiver, the first data rate comprises a lowdata rate defined by the IEEE 802.11ba specification, and the seconddata rate comprises a high data rate defined by the IEEE 802.11baspecification. In some aspects, the first data rate is approximately62.5 kb/s, and the second data rate is approximately 250 kb/s.

FIG. 11 shows an illustrative flow chart depicting another exampleoperation 1100 for determining a data rate of a received packet. Theexample operation 1100 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thereceiving device receives, from the transmitting device, a patterncontained in a preamble of the packet (1102). The receiving devicegenerates a waveform based on a correlation between the received patternand a reference pattern (1104). In some implementations, the receivedpattern comprises one or more instances of a maximal length sequence(MLS), and the reference pattern comprises one or more instances of theMLS or a variant of the MLS (such as a logical complement of the MLS).In some aspects, the reference pattern is derived from the MLS byconverting the 0's of the MLS to −1's, and maintaining the 1's of theMLS.

The receiving device determines a length of the received pattern (1106).The receiving device may determine the length of the received pattern bydetecting a short pattern or a long pattern in the preamble. In someimplementations, the short pattern comprises one maximal length sequence(MLS), and the long pattern comprises a plurality of copies of the MLS.In some aspects, the long pattern comprises at least one copy of the MLSand at least one copy of a logically complemented MLS.

The receiving device determines the data rate based on the determinedlength (1108). In some implementations, detection of the long patternindicates a low data rate, and detection of the short pattern indicatesa high data rate.

FIG. 12A shows an illustrative flow chart depicting an example operation1200 for indicating a data rate of a transmitted packet. The exampleoperation 1200 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thetransmitting device selects the data rate of a data field of the packet(1201). The transmitting device selects a first pattern based on theselected data rate being a first data rate (1202), and selects a secondpattern based on the selected data rate being a second data rate (1203).In some implementations, the first pattern comprises a maximal lengthsequence (MLS), and the second pattern comprises a logical complement ofthe MLS.

The transmitting device embeds either the first pattern or the secondpattern into a preamble of the packet (1204). For example, if theselected data rate is the first data rate, the transmitting deviceembeds the first pattern into the preamble of the packet. If theselected data rate is the second data rate, the transmitting deviceembeds the second pattern into the preamble of the packet. In someaspects, the first data rate comprises a low data rate defined by theIEEE 802.11ba specification, and the second data rate comprises a highdata rate defined by the IEEE 802.11ba specification.

The transmitting device transmits the packet to a receiving device(1205). In some aspects, the transmitting device transmits at least thepreamble of the packet by modulating an OFDM waveform using an ON-OFFkeying modulation scheme.

FIG. 12B shows an illustrative flow chart depicting another exampleoperation 1210 for indicating a data rate of a transmitted packet. Theexample operation 1210 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thetransmitting device may select the data rate of a data field of thepacket (1212). In some implementations, the transmitting device mayselect a low data rate (LDR) of 62.5 kb/s or a high data rate (HDR) of250 kb/s, for example, as provided in the IEEE 802.11ba specification.In other implementations, the transmitting device may select othersuitable data rates.

The transmitting device may select a pattern to embed within a preambleof the packet based on the selected data rate (1214). In someimplementations, the transmitting device may select different patternsto embed within the packet preamble based on the selected data rate. Forexample, FIG. 12C shows an illustrative flow chart depicting an exampleoperation 1220 for selecting a pattern based on the selected data rateof a packet. The transmitting device may select a first structure thatincludes a first number of instances of a sequence or its logicalcomplement if the selected data rate is the low data rate (1222), andmay select a second structure that includes a second number of instancesof the sequence or its logical complement if the selected data rate isthe high data rate (1224). In some implementations, the first structuremay include two instances of the sequence W, and the second structuremay include a single instance of the logically complemented sequence W.In some aspects, the sequence W may be 32 bits long, the first structuremay be 64 bits long, and the second structure may be 32 bits long. Inother implementations, the second structure may also include one or moreinstances of a second sequence or one or more instances of a logicalcomplement of the second sequence. In addition, or in the alternative,the second structure may include one or more instances of a padsequence.

Referring again to FIG. 12B, the transmitting device may transmit thepacket to the receiving device, the preamble of the packet includingeither the first structure or the second structure as the selectedpattern (1216). The transmitting device may embed the selected patternwithin any suitable portion of the packet preamble. In someimplementations, the transmitting device may embed the selected patternwithin the Sync field of a WUR message. In addition, or in thealternative, the transmitting device may transmit the selected patternby modulating an OFDM waveform using an ON-OFF keying modulation scheme.

FIG. 13 shows an illustrative flow chart depicting another exampleoperation 1300 for indicating a data rate of a transmitted packet. Theexample operation 1300 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thetransmitting device selects the data rate of a data field of the packet(1302). The transmitting device selects a length of a preamble based onthe selected data rate (1304). In some implementations, the transmittingdevice selects a short preamble if the selected data rate is a high datarate, and selects a long preamble if the selected data rate is a lowdata rate. The short preamble may contain one copy of an MLS, and thelong preamble may contain a plurality of copies of the MLS or logicalcomplements of the MLS.

The transmitting device embeds either a long pattern or a short patterninto the preamble based on the selected preamble length (1306). In someaspects, the transmitting device embeds the long pattern into thepacket's preamble when the packet is to be transmitted at the low datarate, and embeds the short pattern into the packet's preamble when thepacket is to be transmitted at the high data rate. The transmittingdevice then transmits the packet with the preamble of the selectedlength to a receiving device (1308). In some aspects, the preamble istransmitted by modulating an OFDM waveform using an ON-OFF keyingmodulation scheme.

The short patterns described above each include a single instance of thesequence S or the complemented sequence S, and may be readilydistinguishable from long patterns that include a plurality of instancesof the sequence S or the complemented sequence S. In otherimplementations, the short pattern and the long pattern may each includea plurality of instances of a sequence (such as the sequence S or thecomplemented sequence S). In some aspects, both the short pattern andthe long pattern may be constructed using the same maximum lengthsequence (MLS), for example, so that a wake-up receiver may use a singlecorrelator (such as the correlator 330 of FIG. 3) to correlate eitherthe short pattern or the long pattern with the reference pattern togenerate an output signal. Although the short pattern may include fewerinstances of the sequence than the long pattern, peaks in the outputsignal resulting from the short pattern may have the same timing offsetas peaks in the output signal resulting from the long pattern. Morespecifically, in implementations in which the short pattern and the longpattern each include multiple instances of the same sequence (such asthe sequence S or the complemented sequence S), the spacing betweenpeaks in the output signal will be the same irrespective of whether theshort pattern is correlated with the reference pattern or the longpattern is correlated with the reference pattern. As a result, thewake-up receiver may have more difficulty determining whether a receivedpattern is a short pattern or a long pattern, for example, as comparedto implementations in which the short pattern contains only one instanceof the sequence.

For example, referring again to FIG. 5B, the four large negative peaks514 in the waveform of the correlator output signal 512 are caused bysequentially correlating four instances of the complemented sequence Swith the reference pattern. Because each instance of the complementedsequence S has the same length or duration, the four large negativepeaks 514 in the waveform of the correlator output signal 512 areequally spaced apart in time, for example, such that the time offsetbetween each pair of adjacent peaks 514 is the same. Thus, although thepeak detector 340 may be able to determine that the four large negativepeaks 514 result from correlating the sequences [S, S, S, S] with thereference pattern, the peak detector 340 may not be able to determinewhether the sequences [S, S, S, S] are part of a short pattern or a longpattern, which in turn may reduce the ability of the wake-up receiver todetermine the data rate of a received packet based on the length of thepattern contained in the packet's preamble.

In accordance with aspects of the present disclosure, one or more shortpad sequences may be embedded within the short pattern to increase thespacing between peaks in the output signal resulting from multipleinstances of the sequence S (or the complemented sequence S) containedin the short pattern (as compared to the spacing between peaks in thecorrelator output signal corresponding to multiple instances of thesequence S (or the complemented sequence S) contained in the longpattern). For example, if the duration of the sequence S (and thus theduration of the complemented sequence S) is T μs, then peaks in theoutput signal resulting from multiple instances of the sequence S may beseparated in time by T μs, irrespective of whether the instances of thesequence S are contained in a short pattern or in a long pattern.Similarly, if the duration of the complemented sequence S is T μs, thenpeaks in the output signal resulting from multiple instances of thecomplemented sequence S may be separated in time by T μs, irrespectiveof whether the instances of the sequence S are contained in a shortpattern or in a long pattern.

Thus, by inserting an instance of a pad sequence P having a duration ofΔ μs between each pair of adjacent sequences contained in the shortpattern, peaks in the associated output signal may be separated in timeby T+Δ μs (rather than by T μs). The long pattern may not include anyinstances of the pad sequence P, for example, so that peaks in itsassociated output signal are separated in time by T μs. In this manner,one or more instances of the pad sequence P may be inserted in the shortpattern, but not in the long pattern, so that the timing offset betweenpeaks in the output signal resulting from the short pattern aredifferent than the timing offset between peaks in the output signalresulting from the long pattern. The resulting differences in spacingsbetween peaks in the output signal for the short pattern and the longpattern may allow the wake-up receiver to more easily distinguishbetween a short pattern and a long pattern, which in turn may improveits ability to determine the data rate of a received packet based on thepattern contained in its preamble.

In addition, or in the alternative, one or more short pad sequences maybe embedded within the long pattern to alter the spacing between peaksin the output signal resulting from instances of the sequence S (or thecomplemented sequence S) contained in the long pattern. However, becauseinserting one or more short pad sequences into the long patternincreases the length of the long pattern, it may be desirable to insertthe short pad sequences only into the short pattern, for example,because the length of the short pattern is less than the length of thelong pattern, even after the short pad sequences are inserted into theshort pattern.

The pad sequence P may include any suitable pattern, and may also be ofany suitable length. In some aspects, the pad sequence P may include apattern of alternating 1's and 0's to minimize undesirable logic stateresiduals at the input of the wake-up receiver, although a pattern ofall 1's or all 0's may also be used as the pad sequence P. Further,although the pad sequence P is described in the examples herein asincluding 2 bits, the pad sequence P may include other numbers of bits,for example, as long as the length of the pad sequence does notinadvertently cause the spacing between peaks in the output signalresulting from the short pattern to become equal to the spacing betweenpeaks in the output signal resulting from the long pattern.

In some implementations, the long pattern may be constructed byconcatenating instances or copies of the sequences S and/or S, and theshort pattern may be constructed by concatenating instances or copies ofthe sequences S and/or S and then inserting an instance of the padsequence P between adjacent instances of the sequences S and/or S. Insome aspects, each sequence bit has a duration of 1 μs. For purposes ofdiscussion herein, a 16-bit MLS is selected as the sequence S, a 2-bitpattern is selected as the pad sequence P, the long pattern isconstructed using eight instances of the sequence S and/or thecomplemented sequence S, and the short pattern is constructed usingthree instances of the sequence S and/or the complemented sequence S andtwo instances of the pad sequence P. For example, the 16-bit MLS may beselected as S=[0,1,0,0,0,1,1,1,1,0,1,0,1,1,0,0], the 2-bit patternP=[1,0] may be selected as the pad sequence P, the long pattern mayinclude four copies of the sequence S and four copies of thecomplemented sequence S constructed as LP=[S, S, S, S, S, S, S, S], andthe short pattern may include two copies of the sequence S, one copy ofthe complemented sequence S, and two copies of the pad sequence Pconstructed as SP=[S, P, S, P, S]. For this example, the long pattern LPhas a duration of 128 μs, and the short pattern SP has a duration of 52μs.

It is to be understood that the specific length and pattern of the MLSdescribed herein is merely one of many possible implementations, andtherefore aspects of the present disclosure are not so limited.Similarly, the specific lengths and patterns of the pad sequence P, thelong pattern (LP), and the short pattern (SP) described herein aremerely one of many possible implementations, and therefore aspects ofthe present disclosure are not so limited. Further, the short patternand the long pattern disclosed herein may also be referred to as a shortsync and a long sync, respectively.

FIG. 14 shows a block diagram of an example pattern detector 1400. Thepattern detector 1400 is shown to include a long aggregator 1410, ashort aggregator 1420, a correlator 1430, a first peak detector 1441, asecond peak detector 1442, a reference signal generator 1450, and acomparator 1480. The pattern detector 1400 may be employed by thewake-up receiver 300 of FIG. 3, for example, by coupling an inputterminal of the correlator 1430 to the output of the baseband processor320. In some aspects, the correlator 1430 may be one implementation ofthe correlator 330 of FIG. 3, the first and second peak detectors1441-1442 may be one implementation of the peak detector 340 of FIG. 3,and the reference signal generator 1450 may be one implementation of thereference signal generator 350 of FIG. 3. It is noted that using asingle correlator 1430 in a wake-up receiver (such as the wake-upreceiver 300 of FIG. 3) may not only reduce power consumption but alsoconserve circuit area, for example, as compared with receivers that usedifferent correlators for long preambles and short preambles.

The correlator 1430 includes a first input to receive one or moresequences of a pattern contained in the preamble of a wake-up message,includes a second input to receive the reference pattern R from thereference signal generator 1450, and includes an output coupled toinputs of the long aggregator 1410 and the short aggregator 1420. Thecorrelator 1430 may be configured to correlate each of the receivedsequences with the reference pattern R to generate the correlator outputsignal. The correlator output signal, which is provided to the longaggregator 1410 and to the short aggregator 1420, may include a numberof large positive peaks and/or a number of large negative peaksdepending on the sequences contained in the received pattern. Forexample, when a received sequence S is aligned in time with thereference pattern R, the correlator output signal may include a largepositive peak, for example, because the 1's in the received sequence Sare multiplied by corresponding 1's in the reference pattern R, and the0's in the received sequence S are multiplied by corresponding −1's inthe reference pattern R. When a received complemented sequence S isaligned in time with the reference pattern R, the correlator outputsignal may include a large negative peak, for example, because the 0'sin the received complemented sequence S are multiplied by corresponding1's in the reference pattern R, and the 1's in the received complementedsequence S are multiplied by corresponding −1's in the reference patternR.

The long aggregator 1410 may aggregate multiple peaks in the correlatoroutput signal corresponding to multiple instances of the sequence Sand/or the complemented sequence S contained in a received long patternto generate the long aggregator output signal. The first peak detector1441 includes an input coupled to the output of the long aggregator1410, and may detect a presence of positive peaks or negative peaks inthe long aggregator output signal. In some aspects, the first peakdetector 1441 may use a number of threshold levels to determine whethera particular peak in the long aggregator output signal qualifies aseither a large positive peak or a large negative peak. The long patterndetection signal generated by the first peak detector 1441 may indicatewhether a long pattern was detected in the received wake-up message.

The short aggregator 1420 may aggregate multiple peaks in the correlatoroutput signal corresponding to multiple instances of the sequence Sand/or the complemented sequence S contained in a received short patternto generate a short aggregator output signal. The second peak detector1442 includes an input coupled to the output of the short aggregator1420, and may detect a presence of positive peaks or negative peaks inthe short aggregator output signal. In some aspects, the second peakdetector 1442 may use a number of threshold levels to determine whethera particular peak in the short aggregator output signal qualifies aseither a large positive peak or a large negative peak. The shortaggregator detection signal generated by the second peak detector 1442may indicate whether a short pattern was detected in the receivedwake-up message.

The comparator 1480 includes a first input to receive the long patterndetection signal provided by the first peak detector 1441, a secondinput to receive the short pattern detection signal provided by thesecond peak detector 1442, and an output to provide a data rateindication signal. In some implementations, the comparator 1480 maycompare or otherwise analyze the long pattern detection signal and theshort pattern detection signal to determine which of the long patterndetection signal or the short pattern detection signal includes adominant peak. In some aspects, if the long pattern detection signalincludes a dominant peak and the short pattern detection signal does notinclude a dominant peak, then the comparator 1480 may cause the datarate indication signal to indicate that the received packet wastransmitted at the low data rate. Conversely, if the short patterndetection signal includes a dominant peak and the long pattern detectionsignal does not include a dominant peak, then the comparator 1480 maycause the data rate indication signal to indicate that the receivedpacket was transmitted at the high data rate.

In some implementations, the detection of a long pattern may indicate apresence of a long preamble in the received wake-up message, which inturn may indicate that the wake-up message was transmitted at the lowdata rate. The detection of a short pattern may indicate a presence of ashort preamble in the received wake-up message, which in turn mayindicate that the wake-up message was transmitted at the high data rate.In some aspects, the low data rate is 62.5 kb/s, and the high data rateis 250 kb/s.

FIG. 15A shows a block diagram of an example long aggregator 1500configured to aggregate peaks in the correlator output signal resultingfrom a correlation between a long pattern and the reference pattern R.The long aggregator 1500, which may be one implementation of the longaggregator 1410 of FIG. 14, includes an input to receive a correlatoroutput signal (CS₀), an output to generate the long aggregator outputsignal, a number of series-connected sampling circuits 1510(1)-1510(7),and a summer 1520. Each of the sampling circuits 1510(1)-1510(7) may beconfigured to delay and sample the correlator output signal generated bythe correlator 1430. For example, the first sampling circuit 1510(1)samples the correlator output signal CS₀ provided by the correlator 1430and generates a first delayed correlator signal CS₁, the second samplingcircuit 1510(2) samples the first delayed correlator signal CS₁ andgenerates a second delayed correlator signal CS₂, the third samplingcircuit 1510(3) samples the second delayed correlator signal CS₂ andgenerates a third delayed correlator signal CS₃, and so on, where theseventh sampling circuit 1510(7) samples the sixth delayed signal CS₆and generates a seventh delayed correlator signal CS₇.

For implementations in which the short and long patterns are based on a16-bit MLS having a duration of 16 μs, each of the sampling circuits1510(1)-1510(7) may be configured to introduce a delay of 16 μs and mayhave a sampling rate of 4 MHz. In this manner, each of the samplingcircuits 1510(1)-1510(7) may aggregate peaks every 16 μs*4 MHz=64samples of the correlator output signal, and each of the correlatorsignals CS₁-CS₇ may be delayed by 16 μs relative to the previouscorrelator signal. Thus, in some implementations, the peaks in thecorrelator output signal resulting from sequential instances of thesequence S (or the logically complemented sequence S) in the longpattern are separated in time by 16 μs, and configuration of thesampling circuits 1510(1)-1510(7) results in the long aggregator 1500having a sampling interval of 16 μs. As a result, if the correlatoroutput signal is generated in response to a correlation of the longpattern with the reference pattern, then the peaks in the correlatoroutput signal align with the sampling interval of the long aggregator1500, for example, so that the long aggregator 1500 aggregates all ofthe peaks (or at least most of the peaks) to generate a large dominantpeak. Conversely, if the correlator output signal is generated inresponse to a correlation of the short pattern with the referencepattern, then only one of the peaks in the correlator output signalaligns with the sampling interval of the long aggregator 1500, forexample, so that the long aggregator 1500 does not generating a largedominant peak.

The summer 1520 sums, aggregates, or otherwise combines theincrementally delayed correlator signals CS₀-CS₇ to generate a longaggregator output signal having a dominant peak representative of thesums of the individual peaks in the correlator output signal. Morespecifically, the summer 1520 aggregates or combines individual peaksresulting from different instances of the sequence S (or thecomplemented sequence S) in the long pattern to generate a largedominant peak that can be more easily detected than any of theindividual peaks (particularly at high SNRs levels associated with thelow data rate).

The long aggregator 1500 also includes a number of logic elements 810coupled between selected ones of the sampling circuits 1510(1)-1510(7)and the summer 1520. The logic elements 810 may be configured tomultiply selected ones of the correlator signals CS₀-CS₇ by −1 tocompensate for negative peaks in the correlator output signal caused byinstances of the sequence S in the long pattern LP=[S, S, S, S, S, S, S,S]. For the example long aggregator 1500 of FIG. 15, the logic elements810 are configured to multiple the correlator signals CS₁, CS₂, CS₃, andCS₆ by −1 to compensate for instances of the complemented sequence Sappearing at sequence locations 7, 6, 5, and 2 of the long patternLP=[S, S, S, S, S, S, S, S]. An example of a long aggregator outputsignal generated by the summer 1520 based on a correlation of the longpattern LP=[S, S, S, S, S, S, S, S] with instances of the referencepattern R is depicted in FIG. 16A.

FIG. 15B shows a block diagram of an example short aggregator 1550configured to aggregate peaks in the correlator output signal resultingfrom a correlation between a short pattern and the reference pattern R.The short aggregator 1550, which may be one implementation of the shortaggregator 1420 of FIG. 14, includes an input to receive the correlatoroutput signal CS₀, an output to generate a short aggregator outputsignal, a number of series-connected sampling circuits 1560(1)-1560(2),and a summer 1570. Each of the sampling circuits 1560(1)-1560(2) may beconfigured to delay and sample the correlator output signal generated bythe correlator 1430. For example, the first sampling circuit 1560(1)samples the correlator output signal CS₀ provided by the correlator 1430and generates a first delayed correlator signal CS₁, and the secondsampling circuit 1560(2) samples the first delayed signal CS₁ andgenerates a second delayed correlator signal CS₂.

For implementations in which the short and long patterns are based on a16-bit MLS having a duration of 16 μs and a pad sequence P having aduration of 2 μs, each of the sampling circuits 1560(1)-1560(2) may beconfigured to introduce a delay of 16 μs+2 μs=18 μs and may have asampling rate of 4 MHz. In this manner, each of the sampling circuits1560(1)-1560(2) may aggregate peaks every 18 μs×4 MHz=72 samples of thecorrelator output signal, and each of the correlator signals CS₁-CS₂ maybe delayed by 18 μs relative to the previous correlator signal. Thus, insome implementations, the peaks in the correlator output signalresulting from sequential instances of the sequence S (or thecomplemented sequence S) in the short pattern are separated in time by18 μs, and configuration of the sampling circuits 1560(1)-1560(2)results in the short aggregator 1550 having a sampling interval of 18μs. As a result, if the correlator output signal is generated inresponse to a correlation of the short pattern with the referencepattern, then the peaks in the correlator output signal align with thesampling interval of the short aggregator 1550, for example, so that theshort aggregator 1550 aggregates all of the peaks (or at least most ofthe peaks) to generate a large dominant peak. Conversely, if thecorrelator output signal is generated in response to a correlation ofthe long pattern with the reference pattern, then only one of the peaksin the correlator output signal aligns with the sampling interval of theshort aggregator 1550, for example, so that the short aggregator 1550does not generating a large dominant peak.

The summer 1570 sums, aggregates, or otherwise combines theincrementally delayed correlator signals CS₀-CS₂ to generate a shortaggregator output signal having a dominant peak representative of thesums of peaks in the correlator output signal. More specifically, thesummer 1570 aggregates or combines individual peaks resulting fromdifferent instances of the sequence S (or the complemented sequence S)in the short pattern to generate a large dominant peak that can be moreeasily detected than any of the individual peaks.

The short aggregator 1550 also includes a logic element 810 coupledbetween the output of the first sampling circuit 1560(1) and the summer1570. The logic element 810 is configured to multiply the correlatorsignal CS₁ by −1 to compensate for the negative peak in the correlatoroutput signal caused by the instance of the complemented sequence S inthe short pattern SP=[S, P, S, P, S]. An example of the short aggregatoroutput signal provided by the summer 1570 based on a correlation of theshort pattern SP=[S, P, S, P, S] with instances of the reference patternR is depicted in FIG. 16B.

FIG. 16A shows a graph 1600 depicting an example output waveform 1601generated by the long aggregator 1500 of FIG. 15A based on a correlationof the long pattern LP=[S, S, S, S, S, S, S, S] with instances of thereference pattern R. The output waveform 1601 includes a large“dominant” peak 1602 that represents the sum or combination of eightpeaks in the correlator output signal which correspond to the eightinstances of the sequence S or S in the long pattern. Although not shownfor simplicity, the eight peaks in the correlator output signal areseparated in time by the duration of the sequence S, which for thisexample is 16 μs. Note that the output waveform 1601 includes a numberof small negative peaks 1603 that may correspond to individual peaks inthe correlator output signal that were not aggregated with other peaks,for example, because these peaks 1603 are not aligned with the samplinginterval of the long aggregator 1500.

The graph 1600 also depicts an example output waveform 1605 generated bythe long aggregator 1500 based on a correlation of the short patternSP=[S, P, S, P, S] with instances of the reference pattern R. The outputwaveform 1605 does not include any notable peaks because the sequencescontained in the short pattern are not aligned in time with the samplinginterval of the long aggregator 1500. In some aspects, the outputwaveform 1605 may be a zero-mean waveform, for example, because of thesymmetry of the short pattern SP=[S, P, S, P, S].

FIG. 16B shows a graph 1610 depicting an example output waveform 1611generated by the short aggregator 1550 of FIG. 15B based on acorrelation of the short pattern SP=[S, P, S, P, S] with instances ofthe reference pattern R. The output waveform 1611 includes a large“dominant” peak 1612 that represents the sum or combination of threepeaks in the correlator output signal which correspond to the threeinstances of the sequence S or S in the short pattern. Although notshown for simplicity, the three peaks in the correlator output signalare separated in time by the duration of the sequence S plus theduration of the pad sequence, which for this example is 16 μs+2 μs=18μs. Note that the output waveform 1611 includes a number of smallnegative peaks 1613 that may correspond to individual peaks in thecorrelator output signal that were not aggregated with other peaks, forexample, because these peaks 1613 are not aligned with the samplinginterval of the short aggregator 1550.

The graph 1610 also depicts an example output waveform 1615 generated bythe short aggregator 1550 based on a correlation of the long patternLP=[S, S, S, S, S, S, S, S] with instances of the reference pattern R.The output waveform 1615 may include a number of smaller positive peaks1616 corresponding to individual instances of the sequence S in the longpattern that were not aggregated, and may include a number of smallernegative peaks 1617 corresponding to individual instances of thecomplemented sequence S in the long pattern that were not aggregated,but notably does not include a large dominant peak.

FIG. 17 shows an illustrative flow chart depicting another exampleoperation 1700 for indicating a data rate of a transmitted packet. Theexample operation 1700 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thetransmitting device selects the data rate of a data field of the packet(1702). In some implementations, the transmitting device may selectbetween a low data rate and a high data rate. In some aspects, the lowdata rate is 62.5 kb/s, and the high data rate is 250 kb/s.

The transmitting device selects a pattern to embed within a preamble ofthe packet based on the selected data rate (1704). In someimplementations, the transmitting device selects a long pattern if theselected data rate is the low data rate, the long pattern including afirst number of instances of a sequence or its logical complement(1704A), and selects a short pattern if the selected data rate is thehigh data rate, the short pattern including a second number of instancesof the sequence or its logical complement, and including one or moreinstances of a pad sequence (1704B). In some implementations, thesequence is a maximal length sequence (MLS), and its logical complementis a logically complemented MLS. In some implementations, the padsequence comprises a pattern of alternating 1's and 0's.

In some aspects, the short pattern includes alternating instances of thesequence and the pad sequence, for example, such that an instance of thepad sequence appears between each pair of adjacent sequences in theshort pattern. Each instance of the pad sequence may introduce a timeoffset between a corresponding pair of adjacent sequences, therebyincreasing the separation in time between successive instances of thesequence in the short pattern (as compared to the separation in timebetween successive instances of the sequence in the long pattern). Inthis manner, the separation in time between successive instances of thesequence in the short pattern is greater than the separation in timebetween successive instances of the sequence in the short pattern, whichin turn allows the comparator 1480 of FIG. 14 to determine the data rateof the received packet based on a comparison between the long patterndetection signal and the short pattern detection signal.

The sequence may include any suitable MLS, and may include variouscombinations of instances of the MLS and the logically complemented MLS.The pad sequence may also be of any suitable length, as long as the padsequence length does not cause the separation in time between successiveinstances of the sequence in the short pattern to be similar to theseparation in time between successive instances of the sequence in thelong pattern. In some implementations, the MLS comprises 16 bits, thepad sequence comprises 2 bits, and each of the bits in the MLS and thepad sequence has a duration of 1 μs.

The transmitting device selects a length of the preamble based on theselected data rate (1706). In some implementations, the transmittingdevice selects a long length preamble if the selected data rate is thelow data rate (1706A), and selects a short length preamble if theselected data rate is the high data rate (1706B). In some aspects, thelong preamble is configured to contain the long pattern, and the shortpreamble is configured to contain the short pattern.

The transmitting device then transmits, to a receiving device, thepacket including the preamble containing the selected pattern (1708).The packet may be transmitted by modulating an OFDM waveform using anON-OFF Keying (OOK) modulation scheme. In some aspects, a presence ofthe long pattern in the preamble may indicate that the packet istransmitted at the low data rate, and a presence of the short pattern inthe preamble may indicate that the packet is transmitted at the highdata rate.

FIG. 18 shows an illustrative flow chart depicting another exampleoperation 1800 for determining a data rate of a received packet. Theexample operation 1800 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thereceiving device receives the packet from a transmitting device, thepacket including a preamble containing a pattern comprising at least twoor more instances of a sequence (1802). In some implementations, thepreamble may be a long preamble that contains a long pattern, or may bea short preamble that contains a short pattern. The long pattern mayinclude a first number of instances of a sequence, and the short patternmay include a second smaller number of instances of the sequence and oneor more instances of a pad sequence. In some implementations, thesequence is one of a maximal length sequence (MLS) or a logicallycomplemented MLS. In some implementations, the pad sequence comprises apattern of alternating 1's and 0's.

In some aspects, the short pattern includes alternating instances of thesequence and the pad sequence, for example, such that an instance of thepad sequence appears between each pair of adjacent sequences in theshort pattern. Each instance of the pad sequence introduces a timeoffset between a corresponding pair of adjacent sequences, therebyincreasing the separation in time between successive instances of thesequence in the short pattern (as compared to the separation in timebetween successive instances of the sequence in the long pattern). Inthis manner, the separation in time between successive instances of thesequence in the short pattern is greater than the separation in timebetween successive instances of the sequence in the short pattern.

The receiving device generates a signal based on a correlation betweenthe pattern and a reference sequence (1804). In some implementations,the receiving device may correlate successive instances of the sequence(or the complemented sequence) with a reference pattern to generate thesignal, and the signal may include a peak corresponding to each instanceof the sequence (or the complemented sequence) in the received pattern.In some aspects, a correlation between the sequence and the referencepattern may generate a positive peak in the signal, and a correlationbetween the complemented sequence and the reference pattern may generatea negative peak in the signal.

The receiving device aggregates peaks in the signal using a firstaggregator to generate a first waveform (1806), and aggregates peaks inthe signal using a second aggregator to generate a second waveform(1808). In some implementations, the first aggregator is configured toaggregate peaks in the signal that are separated in time by a firsttiming offset, and the second aggregator is configured to aggregatepeaks in the signal that are separated in time by a second timing offsetthat is greater than the first timing offset.

The receiving device detects a presence of a dominant peak in either thefirst waveform or the second waveform (1810). For one example, if thereceived pattern comprises a long pattern including a number ofsequences separated in time by the first timing offset, then the peaksin the corresponding output signal may align with the sampling intervalof the first aggregator, for example, so that all of the peaks (or atleast most of the peaks) in the signal are aggregated to generate alarge dominant peak. Because the second aggregator is configured tosample the correlator output signal using the second timing offset, thepeaks in the corresponding output signal may not align with the samplinginterval of the second aggregator, for example, so that no more than oneof the peaks is aggregated by the second aggregator.

Conversely, if the received pattern comprises a short pattern includinga number of sequences separated in time by the second timing offset(such as because of the presence of a pad sequence between pairs ofadjacent sequences in the short pattern), then the peaks in the signalmay align with the sampling interval of the second aggregator, forexample, so that all of the peaks (or at least most of the peaks) in thecorrelator output signal are aggregated to generate a large dominantpeak. Because the first aggregator is configured to sample thecorrelator output signal using the first timing offset, the peaks in thesignal may not align with the sampling interval of the first aggregator,for example, so that no more than one of the peaks is aggregated by thefirst aggregator.

The receiving device determines whether the received pattern includes ashort pattern or a long pattern based on the detection (1812). In someimplementations, the presence of a dominant peak in the waveformgenerated by the first aggregator may indicate that the received patterncomprises the long pattern, and the presence of a dominant peak in thewaveform generated by the second aggregator may indicate that thereceived pattern comprises the short pattern.

The receiving device determines the data rate of the received packetbased on the determination (1814). In some aspects, the receiving devicedetermines that the data rate of the packet is the low data rate if thereceived pattern comprises the long pattern, and determines that thedata rate of the packet is the high data rate if the received patterncomprises the short pattern.

In accordance with some other aspects of the present disclosure, theshort pattern may include a single instance of a first sequence S, andthe long pattern may include one or more instances of the first sequenceS or the complemented sequence S, as well as one or more instances of asecond sequence T or the complemented second sequence T, or anycombination thereof. In some aspects, the first sequence S is a 16-bitsequence, the second sequence T is a 16-bit sequence different than thefirst sequence S, and each sequence bit has a duration of 2 μs. Thefirst sequence S and the second sequence T are selected to each haverelatively high auto-correlation properties, and to have relatively highcross-correlation properties.

In some implementations, the short pattern is constructed using a singleinstance of the first sequence S, and the long pattern is constructedusing four total instances: two instances of the complemented firstsequence S, one instance of the second sequence T, and one instance ofthe complemented second sequence T. For the examples disclosed herein,the first sequence S=[0,1,0,1,1,0,0,1,1,1,1,0,1,0,0,0] and the secondsequence T=[1,1,1,0,0,1,0,1,0,1,1,0,1,0,0,0]. Additionally, the shortpattern (SP) includes the first sequence S so that the SP=S, and thelong pattern (LP) includes two copies of the complemented first sequenceS, one copy of the second sequence T, and one copy of the complementedsecond sequence T constructed as LP=[S, T, T, S]. For this example, thelong pattern LP has a transmit duration TX_(LP)=(16 bits)*(4sequences)*(2 μs)=128 μs, and the short pattern SP has a transmitTX_(SP)=(16 bits)*(2 μs)=32 μs.

It is to be understood that the specific length and pattern selected forthe first sequence S and the second sequence T described herein ismerely one of many possible implementations, and therefore aspects ofthe present disclosure are not so limited. Thus, in otherimplementations, other suitable bit patterns may be selected for thefirst sequence S and the second sequence T, and the first sequence S andthe second sequence T may include more than 16 bits or less than 16bits.

FIG. 19 shows a block diagram of another example pattern detector 1900.The pattern detector 1900 is shown to include an aggregator 1910, afirst correlator 1930S, a second correlator 1930T, a first referencesignal generator 1950S, a second reference signal generator 1950T, and apeak detector 1940. The pattern detector 1900 may be employed by thewake-up receiver 300 of FIG. 3, for example, by coupling input terminalsof the first correlator 1930S and the second correlator 1930T to theoutput of the baseband processor 320. In some aspects, the first andsecond correlators 1930S and 1930T, respectively, may each be animplementation of the correlator 330 of FIG. 3, and the peak detector1940 may be an implementation of the peak detector 340 of FIG. 3.

The first reference signal generator 1950S provides a first referencepattern R1 to the first correlator 1930S. In some aspects, the firstreference signal generator 1950S may generate the first referencepattern R1 from the first sequence S using the expression R1=(2×S)−1,for example, so that 1's in the first sequence S appear as 1's in thefirst reference pattern R1, and 0's in the first sequence S appear as−1's in the first reference pattern R1. In addition, or in thealternative, the first reference pattern R1 may be zero mean (such thatit includes equal numbers of 1's and −1's), which in turn may cause thecorrelator output signal to also be zero mean.

The second reference signal generator 1950T provides a second referencepattern R2 to the second correlator 1930T. In some aspects, the secondreference signal generator 1950T may generate the second referencepattern R2 from the second sequence T using the expression R2=(2×T)−1,for example, so that 1's in the second sequence T appear as 1's in thesecond reference pattern R2, and 0's in the second sequence T appear as−1's in the second reference pattern R2. In addition, or in thealternative, the second reference pattern R2 may be zero mean (such thatit includes equal numbers of 1's and −1's), which in turn may cause thecorrelator output signal to also be zero mean.

The first correlator 1930S includes a first input to receive a patterncontained in the preamble of a wake-up message, includes a second inputto receive the first reference pattern R1 from the first referencesignal generator 1950S, and includes an output coupled to a first inputof the aggregator 1910. The first correlator 1930S may be configured tocorrelate a sequence contained in the received pattern with the firstreference pattern R1 to generate a first correlator output signal. Thefirst correlator output signal, which is provided to the aggregator1910, may include a large positive peak when the received patternincludes the first sequence S aligned in time with the first referencepattern R1. The large positive peak may appear in the first correlatoroutput signal because the 1's in the received first sequence S aremultiplied by corresponding 1's in the first reference pattern R1, andthe 0's in the received first sequence S are multiplied by corresponding−1's in the first reference pattern R1. In some implementations, thefirst correlator output signal may be used as a short pattern (SP)detection signal indicative of whether a short pattern was detected inthe received wake-up message.

The second correlator 1930T includes a first input to receive thepattern contained in the preamble of the wake-up message, includes asecond input to receive the second reference pattern R2 from the secondreference signal generator 1950T, and includes an output coupled to asecond input of the aggregator 1910. The second correlator 1930T may beconfigured to correlate each sequence contained in the received patternwith the second reference pattern R2 to generate a second correlatoroutput signal. The second correlator output signal, which is provided tothe aggregator 1910, may include a number of large positive peaks and/ora number of large negative peaks depending on the sequences contained inthe received pattern. For example, when a received second sequence T isaligned in time with the second reference pattern R2, the secondcorrelator output signal may include a large positive peak, for example,because the 1's in the received second sequence T are multiplied bycorresponding 1's in the second reference pattern R2, and the 0's in thereceived second sequence T are multiplied by corresponding −1's in thesecond reference pattern R2. When a received complemented secondsequence T is aligned in time with the second reference pattern R2, thesecond correlator output signal may include a large negative peak, forexample, because the 0's in the received complemented second sequence Tare multiplied by corresponding 1's in the second reference pattern R2,and the 1's in the received complemented second sequence T aremultiplied by corresponding −1's in the second reference pattern R2.Further, when a received complemented first sequence S is aligned intime with the second reference pattern R2, the second correlator outputsignal may include a large negative peak, for example, because the 0'sin the received complemented first sequence S are multiplied bycorresponding 1's in the second reference pattern R2, and the 1's in thereceived complemented first sequence S are multiplied by corresponding−1's in the second reference pattern R2.

The aggregator 1910 may aggregate positive peaks in the first correlatoroutput signal CS₁ corresponding to instances of the first sequence S,negative peaks in the first correlator output signal CS₁ correspondingto instances of the complemented first sequence S, positive peaks in thesecond correlator output signal CS₂ corresponding to instances of thesecond sequence T, and negative peaks in the second correlator outputsignal CS₂ corresponding to the complemented second sequence T containedin a received long pattern. In some aspects, the aggregator 1910 maydetect a presence of the long pattern in the received wake-up message bycombining delayed versions of the first and second correlator outputsignals CS₁ and CS₂, for example, as described in more detail withrespect to FIG. 20.

The peak detector 1940 includes an input coupled to the output of theaggregator 1910, and may detect a presence of positive peaks or negativepeaks in the aggregator output signal. In some aspects, the peakdetector 1940 may use a number of threshold levels to determine whethera particular peak in the aggregator output signal qualifies as either alarge positive peak or a large negative peak. The peak detector 1940 maygenerate a long pattern (LP) detection signal indicative of whether along pattern was detected in the received wake-up message.

In some implementations, the detection of a long pattern may indicate apresence of a long preamble in the received wake-up message, which inturn may indicate that the wake-up message was transmitted at the lowdata rate. The detection of a short pattern may indicate a presence of ashort preamble in the received wake-up message, which in turn mayindicate that the wake-up message was transmitted at the high data rate.In some aspects, the low data rate is 62.5 kb/s, and the high data rateis 250 kb/s.

FIG. 20 shows a block diagram of another example aggregator 2000. Theaggregator 2000, which may be one implementation of the aggregator 1910of FIG. 19, includes a first input to receive the first correlatoroutput signal CS₁ provided by the first correlator 1930S, includes asecond input to receive the second correlator output signal CS₂ providedby the second correlator 1930T, includes a number of sampling circuits2010(1)-2010(3), three logic elements 2011-2013, and a summer 2020. Thesampling circuits 2010(1)-2010(3) may be configured to delay and samplethe correlator output signals. In some implementations, the firstsampling circuit 2010(1) samples the first correlator output signal CS₁provided by the first correlator 1930S and generates a first delayedcorrelator signal CS_(1d), the second sampling circuit 2010(2) samplesthe second correlator output signal CS₂ provided by the secondcorrelator 1930T and generates a second delayed correlator signalCS_(2d1), and the third sampling circuit 2010(3) samples the secondcorrelator output signal CS₂ provided by the second correlator 1930T andgenerates a third delayed correlator signal CS_(2d2).

The first sampling circuit 2010(1) may be configured to introduce adelay of 96 μs and may have a sampling rate of 4 MHz, for example, sothat the first sampling circuit 2010(1) introduces a delay equivalent to96 μs*4 MHz=384 samples of the first correlator output signal CS₁. Thesecond sampling circuit 2010(2) may be configured to introduce a delayof 32 μs and may have a sampling rate of 4 MHz, for example, so that thesecond sampling circuit 2010(2) introduces a delay equivalent to 32 μs*4MHz=128 samples of the second correlator output signal CS₂. The thirdsampling circuit 2010(3) may be configured to introduce a delay of 64 μsand may have a sampling rate of 4 MHz, for example, so that the thirdsampling circuit 2010(3) introduces a delay equivalent to 64 μs*4MHz=256 samples of the second correlator output signal CS₂.

In this manner, peaks in the second correlator output signal CS₂resulting from instances of the first complemented first sequence S, thesecond sequence T, or the complemented second sequence T will align togenerate a large dominant peak if the first correlator output signal CS₁is generated in response to a correlation of the long pattern with thefirst reference pattern R1 and the second correlator output signal CS₂is generated in response to a correlation of the long pattern with thesecond reference pattern R2.

The first logic element 2011 may be configured to multiply thecorrelator output signal CS₁ by −1 to compensate for negative peaks inthe first correlator output signal CS₁ caused by a presence of thecomplemented first sequence S in the long pattern LP=[S, T, T, S]. Thesecond logic element 2012 may be configured to multiply the delayedcorrelator output signal CS_(1d) by −1 to compensate for negative peaksin the first correlator output signal CS₁ caused by the other presenceof the complemented first sequence S in the long pattern LP=[S, T, T,S]. The second logic element 2013 may be configured to multiply thedelayed correlator output signal CS_(2d2) by −1 to compensate fornegative peaks in the second correlator output signal CS₂ caused by apresence of the complemented second sequence T in the long patternLP=[S, T, T, S].

The summer 2020 sums, aggregates, or otherwise combines the firstcorrelator output signal CS₁ and the delayed correlator signals CS_(1d),CS_(2d1), and CS_(2d2) to generate the aggregator output signal having adominant peak representative of the sums of the individual peaks. Morespecifically, the summer 2020 aggregates or combines individual peaksresulting from different instances of the complemented first sequence S,the second sequence T, and/or complemented second sequence T in the longpattern to generate a large dominant peak that can be more easilydetected than any of the individual peaks (particularly at high SNRslevels associated with the low data rate).

FIG. 21A shows a graph 2100 depicting an example waveform 2101 based onan aggregation of correlation output signals based on the correlation ofthe long pattern LP=[S, T, T, S] with instances of the first referencepattern R1 and the second reference pattern R2. For example, the examplewaveform 2101 can represent the aggregator output signal from theaggregator 1910 described above with reference to FIG. 19 when the longpattern is received. The output waveform 2101 includes a large positivepeak 2102 that represents the sum or combination of four peaks in thecorrelator output signals which correspond to the presence of thesequences S, T, T, S in the long pattern.

The graph 2100 also depicts an example output waveform 2105 based on anaggregation of correlation output signals based on the correlation ofthe short pattern SP=S with instances of the first reference pattern R1and the second reference pattern R2. For example, the example waveform2101 can represent the aggregator output signal from the aggregator 1910described above with reference to FIG. 19 when the short pattern isreceived. The output waveform 2105 does not include any notable peaks orat least the peaks are relatively small compared to the large positivepeak 2102 corresponding to the aggregation of peaks resulting from thelong pattern LP=[S, T, T, S ].

FIG. 21B shows a graph 2110 depicting an example waveform 2111 based ona correlation of the short pattern SP=S with the first reference patternRE For example, the example waveform 2111 can represent the correlatoroutput signal from the first correlator 1930S described above withreference to FIG. 19 when a short pattern is received. The outputwaveform 2111 includes a large positive peak 2112 in the firstcorrelator output signal CS₁ resulting from a presence of the firstsequence S in the short pattern.

The graph 2110 also depicts an example output waveform 2115 based on acorrelation of the long pattern LP=[S, T, T, S] with instances of thefirst reference pattern R1. For example, the example waveform 2115 canrepresent the correlator output signal from the first correlator 1930Sdescribed above with reference to FIG. 19 when a long pattern isreceived.

In addition, because the short pattern includes the first sequence S andthe long pattern does not include any instances of the first sequence S,the waveform 2111 based on a correlation of the short pattern SP=S withthe first reference pattern R1 will have a large positive peak, whereasthe output waveform 2115 based on a correlation of the long patternLP=[S, T, T, S] with instances of the first reference pattern R1 willhave negative peaks (such as peaks 2116) but not positive peaks.

FIG. 22 shows an illustrative flow chart depicting another exampleoperation 2200 for indicating a data rate of a transmitted packet. Theexample operation 2200 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thetransmitting device selects the data rate of a data field of the packet(2202). In some implementations, the transmitting device may selectbetween a low data rate and a high data rate. In some aspects, the lowdata rate is 62.5 kb/s, and the high data rate is 250 kb/s.

The transmitting device selects a pattern to embed within a preamble ofthe packet based on the selected data rate (2204). In someimplementations, the transmitting device selects a short pattern if theselected data rate is the high data rate, the short pattern including asingle instance of the first sequence (2204A), and selects a longpattern if the selected data rate is the low data rate, the long patternincluding a plurality of instances of a logical complement of the firstsequence, a second sequence, or a logical complement of the secondsequence (2204B). In some implementations, the first and secondsequences S and T are different from each other, for example, whereS=[0,1,0,1,1,0,0,1,1,1,1,0,1,0,0,0] andT=[1,1,1,0,0,1,0,1,0,1,1,0,1,0,0,0]. In some aspects, the short patternSP=S, and the long pattern LP=[S, T, T, S ].

The transmitting device selects a length of the preamble based on theselected data rate (2206). In some implementations, the transmittingdevice selects a long length preamble if the selected data rate is thelow data rate (2206A), and selects a short length preamble if theselected data rate is the high data rate (2206B). In some aspects, thelong preamble is configured to contain the long pattern, and the shortpreamble is configured to contain the short pattern.

The transmitting device then transmits, to a receiving device, thepacket including the preamble containing the selected pattern (2208).The packet may be transmitted by modulating an OFDM waveform using anON-OFF Keying (OOK) modulation scheme. In some aspects, a presence ofthe long pattern in the preamble may indicate that the packet istransmitted at the low data rate, and a presence of the short pattern inthe preamble may indicate that the packet is transmitted at the highdata rate.

FIG. 23 shows an illustrative flow chart depicting another exampleoperation 2300 for determining a data rate of a received packet. Theexample operation 2300 may be performed by any suitable wireless deviceincluding, for example, the AP 110 of FIG. 1, any of the wirelessdevices WD1-WD4 of FIG. 1, or the wireless device 200 of FIG. 2. Thereceiving device receives, from a transmitting device, a packetincluding a preamble containing a pattern (2302). In someimplementations, the preamble may be a short preamble that contains ashort pattern, or may be a long preamble that contains a long pattern.The short pattern may include a single instance of a first sequence S,and the long pattern may include a plurality of instances of thecomplemented first sequence S, the second sequence T, or thecomplemented second sequence T.

The receiving device generates a first signal based on a correlationbetween the received pattern and a first reference sequence R1 (2304),and generates a second signal based on a correlation between thereceived pattern and a second reference sequence R2 (2306). In someimplementations, the receiving device may use the first correlator 1930Sto correlate the short pattern with the first reference pattern R1. Insome aspects, a large positive peak in the first signal may indicatethat the received pattern is the short pattern.

The receiving device aggregates peaks in the first and second signalsusing an aggregator to generate an output waveform (2308).

The receiving device may determine that the received pattern is a shortpattern based on a presence of a dominant positive peak in the firstsignal (2310), and may determine that the received pattern is a longpattern based on a presence of a dominant positive peak in the outputwaveform (2312). In some implementations, the presence of a dominantpeak in the waveform generated by the first aggregator may indicate thatthe received pattern comprises the long pattern, and the presence of adominant peak in the waveform generated by the second aggregator mayindicate that the received pattern comprises the short pattern.

The receiving device determines the data rate of the received packetbased on whether the received pattern is the short pattern or the longpattern (2314). In some aspects, the receiving device determines thatthe data rate of the packet is the low data rate if the received patternis the long pattern, and determines that the data rate of the packet isthe high data rate if the received pattern comprises the short pattern

FIG. 24 shows a table 2400 depicting an example auto-correlation metricfor the short pattern, example auto-correlation metric for the longpattern, example cross-correlation metric between the short pattern andthe long pattern, and example cross-correlation metric between the longpattern and the short pattern.

FIG. 25 shows an example wake-up receiver (WUR) packet 2500. The WURpacket 2500 is shown to include a preamble 2510 and a body 2520. Thebody 2520 includes a WUR data field 2521. The WUR data field 2521 may beused to carry data to be transmitted from a transmitting device to areceiving device. In some implementations, data contained in the WURdata field 2521 may include a number protocol service data units(PSDUs). In addition, or in the alternative, data contained in the WURdata field 2521 may be encoded using Manchester-based encoding.

The preamble 2510 includes a legacy short training field (L-STF) 2511, alegacy long training field (L-LTF) 2512, a legacy signaling (L-SIG)field 2513, a BPSK-Mark field 2514, and a WUR-Sync field. The L-STF2511, the L-LTF field 2512, and the L-SIG field 2513 may form a legacypreamble 2530. In some implementations, the legacy preamble 2530 may betransmitted using the same bandwidth as a bandwidth used to transmit theWUR-data field 2521. In other implementations, the legacy preamble 2530may be transmitted using a larger bandwidth than the bandwidth used totransmit the WUR-data field 2521. In some aspects, the legacy preamble2530 may be transmitted using a 20 MHz channel, and the WUR-data field2521 may be transmitted using a 4 MHz channel (or any higher bandwidthchannel).

The L-STF 2511 may include information for coarse frequency estimation,automatic gain control, and timing recovery. The L-LTF 2512 may includeinformation for fine frequency estimation, channel estimation, and finetiming recovery. The L-SIG field 2513 may include modulation and codinginformation including, for example, the MCS scheme used by thetransmitting device to wirelessly transmit the WUR packet 2500.

The BPSK-Mark field 2514 may contain a BPSK modulated OFDM symbol.

The WUR-Sync field 2515 may be used to store a pattern that indicatesthe data rate at which the WUR data field 2521 of the WUR packet 2500 istransmitted. The WUR-Sync field 2515 may have a duration that is basedon the data rate of the WUR data field 2521. For example, in someimplementations, the WUR-Sync field 2515 may have a duration of either64 μs or 128 μs depending on the data rate of the WUR data field 2521.As described, the WUR-Sync field 2515 may include a long pattern (havinga duration of 128 μs) to indicate that the WUR data field 2521 istransmitted using the low data rate (such as 62.5 kb/s), and theWUR-Sync field 2515 may include a short pattern (having a duration of 64μs) to indicate that the WUR data field 2521 is transmitted using thehigh data rate (such as 250 kb/s). In some implementations, the longpattern may be a first structure including two instances of the sequenceW (concatenated together to form [W,W]), and the short pattern may be asecond structure including a single instance of the logicallycomplemented sequence W.

During transmission of the WUR packet 2500, a PSDU may be processed andappended to the preamble 2510 as the WUR-Data field 2521. A legacyreceiving device may process and decode the legacy preamble 2530 toassist in the protection of the WUR data, and may process the WUR-Syncfield 2515 to aid in the detection, demodulation, and delivery of thePSDU.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single-chip or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The processes of a method or algorithmdisclosed herein may be implemented in a processor-executable softwaremodule which may reside on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that can be enabled to transfer a computer programfrom one place to another. A storage media may be any available mediathat may be accessed by a computer. By way of example, and notlimitation, such computer-readable media may include RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that may be used to storedesired program code in the form of instructions or data structures andthat may be accessed by a computer. Also, any connection can be properlytermed a computer-readable medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk, and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

What is claimed is:
 1. A method for indicating a data rate of a packet,the method performed by a transmitting device and comprising: selectingthe data rate of a data field of the packet; selecting a sequence;indicating a reference pattern to a receiving device, the referencepattern based on the selected sequence; selecting a first patternincluding two instances of the selected sequence when the selected datarate is a low data rate, the first pattern configured to generate twopositive peaks in a signal based on a correlation between the firstpattern and the reference pattern; selecting a second pattern includingone instance of a logical complement of the selected sequence when theselected data rate is a high data rate, the second pattern configured togenerate one negative peak in the signal based on a correlation betweenthe second pattern and the reference pattern; and transmitting thepacket to the receiving device, the preamble of the packet includingeither the first pattern or the second pattern based on the selecteddata rate.
 2. The method of claim 1, wherein the first number is greaterthan the second number, the low data rate is approximately 62.5 kb/s,and the high data rate is approximately 250 kb/s.
 3. The method of claim1, wherein the second structure further includes one or more instancesof a second sequence or one or more instances of a logical complement ofthe second sequence.
 4. The method of claim 1, wherein the secondstructure further includes one or more instances of a pad sequence. 5.The method of claim 1, wherein the selected pattern is embedded within aSync field of the packet preamble.
 6. The method of claim 1, wherein theselected pattern is transmitted by modulating an OFDM waveform using anON-OFF keying modulation scheme.
 7. The method of claim 1, furthercomprising: selecting a length of the preamble based on the selecteddata rate.
 8. The method of claim 1, wherein the reference pattern isderived from the sequence by: converting each logical low bit of thesequence to a negative one; and converting each logical high bit of thesequence to a positive one.
 9. The method of claim 1, wherein theselected sequence comprises a maximum length sequence (MLS).
 10. Themethod of claim 1, wherein the selected sequence is configured toindicate the first data rate, and the logical complement of the selectedsequence is configured to indicate the second data rate.
 11. The methodof claim 1, wherein the first pattern is configured to generate noise inthe correlation signal when the first pattern and the reference patternare misaligned in time.
 12. A transmitting device, comprising: one ormore processors; and a memory storing instructions that, when executedby the one or more processors, cause the transmitting device to: selecta data rate of a data field of the packet; select a sequence; indicate areference pattern to a receiving device, the reference pattern based onthe selected sequence; select a first pattern including two instances ofthe selected sequence when the selected data rate is a low data rate,the first pattern configured to generate two positive peaks in a signalbased on a correlation between the first pattern and the referencepattern; select a second pattern including one instance of a logicalcomplement of the selected sequence when the selected data rate is ahigh data rate, the second pattern configured to generate one negativepeak in the signal based on a correlation between the second pattern andthe reference pattern; and transmit the packet to the receiving device,the preamble of the packet including either the first pattern or thesecond pattern based on the selected data rate.
 13. The transmittingdevice of claim 12, wherein the first number is greater than the secondnumber, the low data rate is approximately 62.5 kb/s, and the high datarate is approximately 250 kb/s.
 14. The transmitting device of claim 12,wherein the second structure further includes one or more instances of asecond sequence or one or more instances of a logical complement of thesecond sequence.
 15. The transmitting device of claim 12, wherein thesecond structure further includes one or more instances of a padsequence.
 16. The transmitting device of claim 12, wherein the selectedpattern is embedded within a Sync field of the packet preamble.
 17. Thetransmitting device of claim 12, wherein the selected pattern istransmitted by modulating an OFDM waveform using an ON-OFF keyingmodulation scheme.
 18. The transmitting device of claim 12, whereinexecution of the instructions further causes the transmitting device to:select a length of the preamble based on the selected data rate.
 19. Thetransmitting device of claim 8, wherein the reference pattern is derivedfrom the sequence by: converting each logical low bit of the sequence toa negative one; and converting each logical high bit of the sequence toa positive one.
 20. The transmitting device of claim 12, wherein theselected sequence comprises a maximum length sequence (MLS).
 21. Themethod of claim 1, wherein the selected sequence is configured toindicate the first data rate, and the logical complement of the selectedsequence is configured to indicate the second data rate.
 22. Thetransmitting device of claim 12, wherein the first pattern is configuredto generate noise in the correlation signal when the first pattern andthe reference pattern are misaligned in time.
 23. A non-transitorycomputer-readable medium storing one or more programs containinginstructions that, when executed by one or more processors of anapparatus, cause the apparatus to perform operations comprising:selecting a data rate of a data field of a packet to be transmitted to areceiving device selecting a sequence; indicating a reference pattern tothe receiving device, the reference pattern based on the selectedsequence; selecting a first pattern including two instances of theselected sequence when the selected data rate is a low data rate, thefirst pattern configured to generate two positive peaks in a signalbased on a correlation between the first pattern and the referencepattern; selecting a second pattern including one instance of a logicalcomplement of the selected sequence when the selected data rate is ahigh data rate, the second pattern configured to generate one negativepeak in the signal based on a correlation between the second pattern andthe reference pattern; and transmitting the packet to the receivingdevice, the preamble of the packet including either the first pattern orthe second pattern based on the selected data rate.
 24. Thenon-transitory computer-readable medium of claim 23, wherein the firstnumber is greater than the second number, the low data rate isapproximately 62.5 kb/s, and the high data rate is approximately 250kb/s.
 25. The non-transitory computer-readable medium of claim 23,wherein the second structure further includes one or more instances of asecond sequence or one or more instances of a logical complement of thesecond sequence.
 26. The non-transitory computer-readable medium ofclaim 23, wherein the second structure further includes one or moreinstances of a pad sequence.
 27. The non-transitory computer-readablemedium of claim 23, wherein the selected pattern is embedded within aSync field of the packet preamble.
 28. The non-transitorycomputer-readable medium of claim 23, wherein execution of theinstructions causes the apparatus to perform operations furthercomprising: selecting a length of the preamble based on the selecteddata rate.
 29. The non-transitory computer-readable medium of claim 23,wherein the reference pattern is derived from the sequence by:converting each logical low bit of the sequence to a negative one; andconverting each logical high bit of the sequence to a positive one. 30.An apparatus, comprising: means for selecting a data rate of a datafield of a packet to be transmitted to a receiving device; means forselecting a sequence; means for indicating a reference pattern to thereceiving device, the reference pattern based on the selected sequence;means for selecting a first pattern including two instances of theselected sequence when the selected data rate is a low data rate, thefirst pattern configured to generate two positive peaks in a signalbased on a correlation between the first pattern and the referencepattern; means for selecting a second pattern including one instance ofa logical complement of the selected sequence when the selected datarate is a high data rate, the second pattern configured to generate onenegative peak in the signal based on a correlation between the secondpattern and the reference pattern; and means for transmitting the packetto the receiving device, the preamble of the packet including either thefirst pattern or the second pattern based on the selected data rate.